fbcon: font setting should check limitation of driver

fbcon_set_font() will now check if the new font dimensions can be drawn by the
driver (by checking pixmap.blit_x and blit_y).  Similarly, add 2 new
parameters to get_default_font(), font_w and font_h, to further aid in the
font selection process.

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>