Add "RECOVERY_24_BIT := true" to the device's BoardConfig.mk to use
24-bit framebuffers in the recovery ui.
Change-Id: Iaede138bf7870becf237f12f1c0e49c9ff82d007
Make ui_init() clear the framebuffer memory it maps in so the user
isn't treated to a visible flash of random bits on recovery startup.
Call ui_set_background() (to show the installing icon) right after
ui_init() to display something while device_recovery_start() is
working (which can take a second or two on some devices).
Bug: 3145331
Change-Id: I11e7859fab5847370ea4f4932c3fb1558af26c5d
