Add common serial driver for Atmel AT32 and AT91 chips

Patch by Haavard Skinnemoen, 06 Sep 2006

This is a first attempt at creating a common serial driver for Atmel
chips. For now, it supports the AT32AP7000 AVR32 chip, but it should
be possible to support AT91RM9200 and other ARM-based chips with some
minor modifications.

There's nothing fundamentally AVR32-specific in this driver, but it
does use some features which are currently only defined for the
AT32AP CPU port:
  * pm_get_clock_freq: Obtain the clock frequency of a given domain
  * gd->console_uart: A "struct device" containing information about
    register mappings, gpio resources and clocks associated with the
    UART device.

For more information about these features, please see the "AT32AP
CPU" patch.