[PATCH] atmel_serial: Support AVR32

Make CONFIG_SERIAL_ATMEL selectable on AVR32 and #ifdef out some ARM-
specific code in the driver.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Acked-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>