[AVR32] Provide more CPU information in /proc/cpuinfo and dmesg

Add the following fields to /proc/cpuinfo:
  * chip type and revision (from the JTAG chip id)
  * cpu MHz (from clk_get_rate())
  * features (from the CONFIG0 register)

Also rename "cpu family" to "cpu arch" and "cpu type" to "cpu core" to
remove some ambiguity.

Show chip type and revision at bootup, and clarify that the other
kinds of IDs that we're already printing are for the cpu core and
architecture. Rename "AP7000" to "AP7" since that's the name of the
core.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>