OMAP: DSS2: Remove FB_OMAP_BOOTLOADER_INIT support

FB_OMAP_BOOTLOADER_INIT does not work, and it was only partially
implemented for SDI.

This patch removes support for FB_OMAP_BOOTLOADER_INIT to clean up the
code and to remove any assumptions that FB_OMAP_BOOTLOADER_INIT would
work.

Proper implementation is much more complex, requiring early boot time
register and clock handling to keep the DSS running.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>