lcd: logo: move generic cmap setting to lcd_logo_set_cmap()

Get rid of platform-specific #ifdefs in bitmap_plot() by moving the generic
case of setting cmap into the weak lcd_logo_set_cmap().

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Bo Shen <voice.shen@atmel.com>
Tested-by: Josh Wu <josh.wu@atmel.com>
Cc: Bo Shen <voice.shen@atmel.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Anatolij Gustschin <agust@denx.de>