ENGR00277843-01 mxsfb: Allocate frame buffer from DMA pool

ENGR00277843-01 mxsfb: Allocate frame buffer from DMA pool

- Original frame buffer size is fixed in SZ_2M when driver probing,
  that can not support more resolution, such as 720p and 1080p.
  Add function mxsfb_map_videomem/mxsfb_unmap_videomem to replace
  fixed frame buffer size. Frame buffer size can change with resolution
  change and application requirement.
- Add fb_mmap function implement.
- Remove member variable sync from struct mxsfb_info, align the sync
  definition with mxc_cea_mode[] in mxc_edid.c.
- Set recovery from underflow bit.
- Fix xres_virtual yres_virtual check issue in function mxsfb_check_var().

Signed-off-by: Sandor Yu <R01008@freescale.com>