svgalib: move fb_get_caps to svgalib

Move fb_get_caps() method to svgalib.c as svga_get_caps() so it can be used by
s3fb, arkfb and vt8623fb.

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>