common lcd: simplify lcd_display_bitmap

Move highly platform dependant code into its own functions to reduce the
number of #ifdefs in lcd_display_bitmap

To avoid breaking the mcc200 board which does not #define
CONFIG_CMD_BMP, this patch also implements bmp_display() for mcc200.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>