Add workaround for 402 signature issue

Naturally when I reopened the issue, what had seemed intractable became
obvious. Fix #67.

megaavr/boards.txt

@@ -131,6 +131,7 @@ atxy7.bootloader.SYSCFG1=0x03
 atxy7.bootloader.APPEND=0x00
 atxy7.bootloader.BOOTEND=0x00
 
+atxy7.upload.workaround=
 
 ##############################################################
 
@@ -256,6 +257,8 @@ atxy6.bootloader.SYSCFG1=0x03
 atxy6.bootloader.APPEND=0x00
 atxy6.bootloader.BOOTEND=0x00
 
+atxy6.upload.workaround=
+
 ##############################################################
 
 atxy4.name=ATtiny1614/1604/814/804/414/404/214/204
@@ -384,6 +387,8 @@ atxy4.bootloader.SYSCFG1=0x03
 atxy4.bootloader.APPEND=0x00
 atxy4.bootloader.BOOTEND=0x00
 
+atxy4.upload.workaround=
+
 ##############################################################
 
 atxy2.name=ATtiny412/402/212/202
@@ -392,26 +397,37 @@ atxy2.name=ATtiny412/402/212/202
 #atxy2.menu.chip.812.build.mcu=attiny812
 #atxy2.menu.chip.812.upload.maximum_size=8192
 #atxy2.menu.chip.812.upload.maximum_data_size=512
+#atxy2.menu.chip.812.upload.workaround=
 atxy2.menu.chip.412=ATtiny412
 atxy2.menu.chip.412.build.mcu=attiny412
 atxy2.menu.chip.412.upload.maximum_size=4096
 atxy2.menu.chip.412.upload.maximum_data_size=256
+atxy2.menu.chip.412.upload.workaround=
 atxy2.menu.chip.212=ATtiny212
 atxy2.menu.chip.212.build.mcu=attiny212
 atxy2.menu.chip.212.upload.maximum_size=2048
 atxy2.menu.chip.212.upload.maximum_data_size=128
+atxy2.menu.chip.212.upload.workaround=
 #atxy2.menu.chip.802=ATtiny802
 #atxy2.menu.chip.802.build.mcu=attiny802
 #atxy2.menu.chip.802.upload.maximum_size=8192
 #atxy2.menu.chip.802.upload.maximum_data_size=512
+#atxy2.menu.chip.802.upload.workaround=
 atxy2.menu.chip.402=ATtiny402
 atxy2.menu.chip.402.build.mcu=attiny402
 atxy2.menu.chip.402.upload.maximum_size=4096
 atxy2.menu.chip.402.upload.maximum_data_size=256
+atxy2.menu.chip.402.upload.workaround=
+atxy2.menu.chip.402w=ATtiny402 (bad signature)
+atxy2.menu.chip.402w.build.mcu=attiny402
+atxy2.menu.chip.402w.upload.maximum_size=4096
+atxy2.menu.chip.402w.upload.maximum_data_size=256
+atxy2.menu.chip.402w.upload.workaround=w
 atxy2.menu.chip.202=ATtiny202
 atxy2.menu.chip.202.build.mcu=attiny202
 atxy2.menu.chip.202.upload.maximum_size=2048
 atxy2.menu.chip.202.upload.maximum_data_size=128
+atxy2.menu.chip.202.upload.workaround=
 
 atxy2.menu.clock.20=20 MHz
 atxy2.menu.clock.16=16 MHz

megaavr/platform.txt

@@ -123,7 +123,7 @@ tools.avrdude.upload.params.quiet=-q -q
 # tools.avrdude.upload.verify is needed for backwards compatibility with IDE 1.6.8 or older, IDE 1.6.9 or newer overrides this value
 tools.avrdude.upload.verify=
 tools.avrdude.upload.params.noverify=-V
-tools.avrdude.upload.pattern="{cmd.path}" "-C{config.path}" {upload.verbose} -p{build.mcu} -c{upload.protocol} -P{serial.port} -e "-Uflash:w:{build.path}/{build.project_name}.hex:i"
+tools.avrdude.upload.pattern="{cmd.path}" "-C{config.path}" {upload.verbose} -p{build.mcu}{upload.workaround} -c{upload.protocol} -P{serial.port} -e "-Uflash:w:{build.path}/{build.project_name}.hex:i"
 
 tools.avrdude.program.params.verbose=-v
 tools.avrdude.program.params.quiet=-q -q