OvmfPkg/QemuVideoDxe: Helper functions for unaligned port I/O.

The VMWare SVGA display device implemented by Qemu (-vga vmware) uses
an I/O-type BAR which is laid out such that some register offsets are
not aligned to the read/write width with which they are expected to be
accessed. (The register value port has an offset of 1 and requires
32 bit wide read/write access.)

The EFI_PCI_IO_PROTOCOL's Io.Read/Io.Write functions do not support
such unaligned I/O.

Before a driver for this device can be added to QemuVideoDxe, helper
functions for unaligned I/O are therefore required. This adds the
functions UnalignedIoWrite32 and UnalignedIoRead32, based on IoLib's
IoWrite32 and IoRead32, for the Ia32 and X64 architectures. Port I/O
requires inline assembly, so implementations are provided for the GCC,
ICC, and Microsoft compiler families. Such I/O is not possible on other
architectures, a dummy (ASSERT()ing) implementation is therefore
provided to satisfy the linker.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Suggested-by: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

OvmfPkg/QemuVideoDxe/QemuVideoDxe.inf

@@ -41,6 +41,12 @@
 
 [Sources.Ia32, Sources.X64]
   VbeShim.c
+  UnalignedIoGcc.c    | GCC
+  UnalignedIoMsc.c    | MSFT
+  UnalignedIoIcc.c    | INTEL
+
+[Sources.IPF, Sources.EBC, Sources.ARM, Sources.AARCH64]
+  UnalignedIoUnsupported.c
 
 [Packages]
   MdePkg/MdePkg.dec