Basic PWM driver for AVR32 and AT91

PWM device setup, and a simple PWM driver exposing a programming interface
giving access to each channel's full capabilities.  Note that this doesn't
support starting several channels in synch.

[hskinnemoen@atmel.com: allocate platform device dynamically]
[hskinnemoen@atmel.com: Kconfig fix]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>