[ARM] pxa: add generic PWM backlight driver

Patch mostly from Eric Miao, with minor edits by rmk to convert
Eric's driver to a generic PWM-based backlight driver.

Signed-off-by: eric miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
4 files changed