OvmfPkg/PlatformPei: parse "X-PciMmio64Mb" with QemuFwCfgSimpleParserLib

OvmfPkg/PlatformPei: parse "X-PciMmio64Mb" with QemuFwCfgSimpleParserLib

Replace the

- QemuFwCfgFindFile(),
- QemuFwCfgSelectItem(),
- QemuFwCfgReadBytes(),
- AsciiStrDecimalToUint64()

sequence in the GetFirstNonAddress() function with a call to
QemuFwCfgSimpleParserLib.

This change is compatible with valid strings accepted previously.

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: <20200424075353.8489-3-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>