lcd: atmel: introduce lcd_logo_set_cmap

Reduce the bitmap_plot #ifdef complexity by extracting Atmel-specific code for
setting cmap into a new function lcd_logo_set_cmap(), which is implemented in
atmel_lcdfb driver and defined as part of common/lcd.c api with a weak dummy
version. In the Atmel implementation, ARRAY_SIZE(bmp_logo_palette) is
switched for BMP_LOGO_COLORS to avoid having to include bmp_logo_data.h, which
would cause a compilation error because the logo data and palette arrays would
be defined twice.

This is a step towards cleaning bitmap_plot() of platform-specific code.

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>