backlight: lp855x: add FAST bit description for LP8556

LP8556 backlight driver supports fast refresh mode when exiting the low
power mode.  This bit can be configurable in the platform side.
Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/platform_data/lp855x.h

@@ -46,6 +46,8 @@
 #define LP8556_I2C_CONFIG	((ENABLE_BL << BL_CTL_SHFT) | \
 				(LP8556_I2C_ONLY << BRT_MODE_SHFT))
 #define LP8556_COMB2_CONFIG	(LP8556_COMBINED2 << BRT_MODE_SHFT)
+#define LP8556_FAST_CONFIG	BIT(7) /* use it if EPROMs should be maintained
+					  when exiting the low power mode */
 
 enum lp855x_chip_id {
 	LP8550,