x86/gpu: Add vfunc for Intel graphics stolen memory base address

x86/gpu: Add vfunc for Intel graphics stolen memory base address

For gen2 devices we're going to need another way to determine
the stolen memory base address. Make that into a vfunc as well.

Also drop the bogus inline keyword from gen8_stolen_size().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Link: http://lkml.kernel.org/r/1391628540-23072-2-git-send-email-ville.syrjala@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>