drivers/video: add Hyper-V Synthetic Video Frame Buffer Driver

This is the driver for the Hyper-V Synthetic Video, which supports
screen resolution up to Full HD 1920x1080 on Windows Server 2012 host,
and 1600x1200 on Windows Server 2008 R2 or earlier.  It also solves the
double mouse cursor issue of the emulated video mode.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Cc: Olaf Hering <olaf@aepfle.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>