Fix off-by-one errors truncating the last byte of FLASH and DATA

[chschu]

When simulating the official optiboot_atmega328.hex bootloader using run_avr -m atmega328 optiboot_atmega328.hex, the following output is produced:

MCU type and frequency are not set when loading .hex file
read_ihex_chunks: optiboot_atmega328.hex, unsupported check type 03
Loaded 476 bytes of Flash data at 0x7e00
Loading 2 bytes of Flash data at 7ffe would overflow buffer (32767 bytes).
Loaded 1 bytes of Flash data at 0x7ffe

The very last byte of FLASH (Optiboot stores its own version there) is never loaded by simavr. The same is true for DATA.

Two of the length calculations in avr_load_firmware(...) are off by one: avr->flashend is the last valid flash address, not the flash size, and avr->ramend is the last valid RAM address, not the RAM size.

This Pull Request fixes the two off-by-one errors. With the change applied, the above command loads the last byte and produces the following output:

MCU type and frequency are not set when loading .hex file
read_ihex_chunks: optiboot_atmega328.hex, unsupported check type 03
Loaded 476 bytes of Flash data at 0x7e00
Loaded 2 bytes of Flash data at 0x7ffe

[gatk555]

Thanks. Not seen in examples/board_simduino, but that bootloader is very old!