hgafb: convert to new platform driver API

Convert the hgafb driver to use new platform driver API.

Addresses http://bugzilla.kernel.org/show_bug.cgi?id=9689



Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: Anton Vorontsov <avorontsov@ru.mvista.com>
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>