tgafb: fix mode setting with fbset

tgafb: fix mode setting with fbset

Mode setting in the TGA driver is broken for these reasons:

- info->fix.line_length is set just once in tgafb_init_fix function. If
  we change videomode, info->fix.line_length is not recalculated - so
  the video mode is changed but the screen is corrupted because of wrong
  info->fix.line_length.

- info->fix.smem_len is set in tgafb_init_fix to the size of the default
  video mode (640x480). If we set a higher resolution,
  info->fix.smem_len is smaller than the current screen size, preventing
  the userspace program from mapping the framebuffer.

This patch fixes it:

- info->fix.line_length initialization is moved to tgafb_set_par so that
  it is recalculated with each mode change.

- info->fix.smem_len is set to a fixed value representing the real
  amount of video ram (the values are taken from xfree86 driver).

- add a check to tgafb_check_var to prevent us from setting a videomode
  that doesn't fit into videoram.

- in tgafb_register, tgafb_init_fix is moved upwards, to be called
  before fb_find_mode (because fb_find_mode already needs the videoram
  size set in tgafb_init_fix).

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vga.kernel.org
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>