gma: Add a HW.PCI.Dev for dynamic MMIO setup

Remove `MMIO_Base` option from Initialize() and try to derive it
using libhwbase' PCI mechanism instead.

Change-Id: Iacd4d098954bb96c1c6b40fdfb2636191d9517c7
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/20600
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/common/hw-gfx-gma.ads b/common/hw-gfx-gma.ads
index c8fc398..8285dcb 100644
--- a/common/hw-gfx-gma.ads
+++ b/common/hw-gfx-gma.ads
@@ -62,8 +62,7 @@
    VGA_PLANE_FRAMEBUFFER_OFFSET : constant := 16#ffff_ffff#;
 
    procedure Initialize
-     (MMIO_Base   : in     Word64 := 0;
-      Write_Delay : in     Word64 := 0;
+     (Write_Delay : in     Word64 := 0;
       Clean_State : in     Boolean := False;
       Success     :    out Boolean)
    with