fb: i.MX IPU: move fb_info initialization to a single function
The bitfield information was only added to fb_info when the
framebuffer actually was enabled. That made it impossible to
call 'bmp' before enabling the display.
So, move all fb_info init to a single place and make it a function
to better allow for multiple displays later.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>