Fix build with current EDK2 master

Re-add the missing headers for EFI_LEGACY_BIOS_PROTOCOL and gEfiLegacyBiosGuid which were removed from OvmfPkg in tianocore/edk2@9d4becd.

Neither OVMF nor EfiGuard actually *needs* the CSM for anything, but being able to check for the presence of the legacy BIOS protocol is still important in order to determine if we are actually booting a legacy BIOS boot option. This allows us to then inform the user that what they are doing is not suppported and most likely a mistake.

Fixes #119

Author: Mattiwatti

Application/Loader/Loader.inf

@@ -14,7 +14,6 @@
   MdePkg/MdePkg.dec
   EfiGuardPkg/EfiGuardPkg.dec
   MdeModulePkg/MdeModulePkg.dec
-  OvmfPkg/OvmfPkg.dec
 
 [LibraryClasses]
   UefiApplicationEntryPoint

EfiGuardPkg.dec

@@ -16,3 +16,10 @@
 [Protocols]
   ## Include/Protocol/EfiGuard.h
   gEfiGuardDriverProtocolGuid    = { 0x51e4785b, 0xb1e4, 0x4fda, { 0xaf, 0x5f, 0x94, 0x2e, 0xc0, 0x15, 0xf1, 0x7 }}
+
+  ## Originally in OvmfPkg/Csm/Include/Protocol/LegacyBios.h
+  gEfiLegacyBiosProtocolGuid     = { 0xdb9a1e3d, 0x45cb, 0x4abb, {0x85, 0x3b, 0xe5, 0x38, 0x7f, 0xdb, 0x2e, 0x2d }}
+
+[Guids]
+  ## Originally in OvmfPkg/Csm/Include/Guid/LegacyBios.h
+  gEfiLegacyBiosGuid             = { 0x2e3044ac, 0x879f, 0x490f, {0x97, 0x60, 0xbb, 0xdf, 0xaf, 0x69, 0x5f, 0x50 }}

Include/Guid/LegacyBios.h

@@ -0,0 +1,24 @@
+#ifndef _LEGACY_BIOS_H_
+#define _LEGACY_BIOS_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+///
+/// The Global ID for the Legacy BIOS GUID that must be installed onto the ImageHandle
+/// of any module follows the EFI Driver Model and uses the Int86() or FarCall()
+/// services of the Legacy BIOS Protocol to produce a standard UEFI I/O Protocol.
+///
+#define EFI_LEGACY_BIOS_GUID \
+	{ \
+	0x2e3044ac, 0x879f, 0x490f, {0x97, 0x60, 0xbb, 0xdf, 0xaf, 0x69, 0x5f, 0x50 } \
+	}
+
+extern EFI_GUID	gEfiLegacyBiosGuid;
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif