OvmfPkg: introduce QemuFwCfgSimpleParserLib

We already parse some boolean and integer values from named fw_cfg files
(usually into PCDs), and we're going to cover more. Add a dedicated
library for centralizing the parsing logic.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Per Sundstrom <per_sundstrom@yahoo.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2681
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200424075353.8489-2-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

OvmfPkg/OvmfPkg.dec

@@ -60,6 +60,10 @@
   #
   QemuFwCfgS3Lib|Include/Library/QemuFwCfgS3Lib.h
 
+  ##  @libraryclass  Parse the contents of named fw_cfg files as simple
+  #                  (scalar) data types.
+  QemuFwCfgSimpleParserLib|Include/Library/QemuFwCfgSimpleParserLib.h
+
   ##  @libraryclass  Rewrite the BootOrder NvVar based on QEMU's "bootorder"
   #                  fw_cfg file.
   #