backlight: add ams369fg06 amoled driver

backlight: add ams369fg06 amoled driver

Add the ams369fg06 amoled panel driver.  The ams369fg06 amoled panel (480
x 800) driver uses 3-wired SPI inteface.  The brightness can be controlled
by gamma setting of amoled panel.

[sfr@canb.auug.org.au: fix build error]
[axel.lin@gmail.com: unregister backlight device when unloading the module]
[axel.lin@gmail.com: staticize ams369fg06_shutdown]
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: anish singh <anish198519851985@gmail.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>