cirrusfb: convert to generic boolean

Convert to generic boolean.

Signed-off-by: Richard Knutsson <ricknu-0@student.ltu.se>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>