[WIN32SS:ENG] Rework EngpUpdateGraphicsDeviceList

- choose VGA adapter outside of driver initialization loop
- choose primary adapter outside of driver initialization loop
- link VGA adapter to primary adapter at the end
- only set DISPLAY_DEVICE_PRIMARY_DEVICE in this function

Also mark VgaSave driver as SystemStart instead of Disabled,
so it is available if main display driver doesn't work.

boot/bootdata/hiveinst.inf

@@ -7,6 +7,3 @@ Signature = "$Windows NT$"
 ;
 ; Display driver section
 ;
-
-; VGA miniport driver
-HKLM,"SYSTEM\CurrentControlSet\Services\VgaSave","Start",0x00010001,0x00000001