OvmfPkg/GenericQemuLoadImageLib: Read cmdline from QemuKernelLoaderFs

Remove the QemuFwCfgLib interface used to read the QEMU cmdline
(-append argument) and the initrd size.  Instead, use the synthetic
filesystem QemuKernelLoaderFs which has three files: "kernel", "initrd",
and "cmdline".

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Tobin Feldman-Fitzthum <tobin@linux.ibm.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Message-Id: <20210628105110.379951-5-dovmurik@linux.ibm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.inf

@@ -25,14 +25,15 @@
 
 [LibraryClasses]
   DebugLib
+  FileHandleLib
   MemoryAllocationLib
   PrintLib
-  QemuFwCfgLib
   UefiBootServicesTableLib
 
 [Protocols]
   gEfiDevicePathProtocolGuid
   gEfiLoadedImageProtocolGuid
+  gEfiSimpleFileSystemProtocolGuid
 
 [Guids]
   gQemuKernelLoaderFsMediaGuid