x86: reserve pages when SandyBridge integrated graphics

x86: reserve pages when SandyBridge integrated graphics

SNB graphics devices have a bug that prevent them from accessing certain
memory ranges, namely anything below 1M and in the pages listed in the
table.

Xen does not initialize below 1MB to heap, i.e. below 1MB pages don't be
allocated, so it's unnecessary to reserve memory below the 1 MB mark
that has not already been reserved.

So reserve those pages listed in the table at xen boot if set detect a
SNB gfx device on the CPU to avoid GPU hangs.

Signed-off-by: Xudong Hao <xudong.hao@intel.com>
Acked-by: Keir Fraser <keir@xen.org>