boards/avr-rss2: Refactor avrdude conf

boards/avr-rss2/Makefile.include

@@ -3,18 +3,8 @@ PORT_LINUX  ?= /dev/ttyUSB0
 PORT_DARWIN ?= $(firstword $(sort $(wildcard /dev/tty.usbmodem*)))
 # refine serial port information for pyterm
 BAUD        ?= 115200
-include $(RIOTMAKE)/tools/serial.inc.mk
+AVR_RSS2_BOOTLOADER ?= stk500v2
+BOOTLOADER  ?= $(AVR_RSS2_BOOTLOADER)
+BOOTLOADER_SIZE ?= 4K # Unlike the Arduino Mega2560, the bootloader size is 4K
 
-# PROGRAMMER defaults to wiring which is the internal flasher via USB
-# using avrdude. Can be overridden for debugging (which requires changes
-# that require to use an ISP)
-PROGRAMMER ?= stk500v2
-#
-# see /usr/include/asm-generic/termbits.h for availabel baudrates on your linux system
-
-# From current fuse configuration
-BOOTLOADER_SIZE ?= 4K
-ROM_RESERVED ?= $(BOOTLOADER_SIZE)
-
-include $(RIOTMAKE)/tools/avrdude.inc.mk
 include $(RIOTBOARD)/common/atmega/Makefile.include