Make lcd_set_enable_hook() conditional on HAVE_LCD_ENABLE and HAVE_LCD_COLOR

This prepares for the Clip which will define HAVE_LCD_ENABLE but won't
need the hook since the internal LCD framebuffer is updated regardless
if the display is on or off.

firmware/drivers/lcd-16bit.c has not been modified since HAVE_LCD_COLOR
is obviously defined here

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@18951 a1c6a512-1295-4272-9138-f99709370657
6 files changed