uart: refactor uart udr write operation outside generic uart write.

	modified:   simavr/sim/avr_uart.c
core: Removed trace crash macro

Made it a function instead.

Reworked from nnayo's commit
core: Handle EIND register

Parts with more than 128KB of flash need an extra byte on the stack
Rework from nnayo branch for the atmega2560

Signed-off-by: Michel Pollet <buserror@gmail.com>
cores: Add atmega2560
Merge pull request #54 from bsekisser/uart-udr-write-changes

uart: refactor uart udr write operation outside generic uart write.