fbdev: kill fb_rotate

fbdev: kill fb_rotate

The fb_rotate method in struct fb_ops is never actually invoked, and
it's been that way in the entire history of git (in fact, the last
occurrence of the string '->fb_rotate' vanished over 10 years ago,
with b4d8aea6d6, and that merely tested whether the callback
existed). So remove some dead code and make struct fb_obs a little
smaller.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>