OvmfPkg: PlatformBootManagerLibGrub: Allow executing kernel via fw_cfg

Support QEMU's -kernel option.

Create a QemuKernel.c for PlatformBootManagerLibGrub
which is an exact copy of the file
PlatformBootManagerLib/QemuKernel.c .

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ashish Kalra <ashish.kalra@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.h

@@ -172,4 +172,15 @@ PlatformInitializeConsole (
   IN PLATFORM_CONSOLE_CONNECT_ENTRY   *PlatformConsole
   );
 
+/**
+  Loads and boots UEFI Linux via the FwCfg interface.
+
+  @retval    EFI_NOT_FOUND - The Linux kernel was not found
+
+**/
+EFI_STATUS
+TryRunningQemuKernel (
+  VOID
+  );
+
 #endif // _PLATFORM_SPECIFIC_BDS_PLATFORM_H_