OvmfPkg/PlatformPei: use QemuFwCfgParseBool in UPDATE_BOOLEAN_PCD_FROM_...

OvmfPkg/PlatformPei: use QemuFwCfgParseBool in UPDATE_BOOLEAN_PCD_FROM_...

The UPDATE_BOOLEAN_PCD_FROM_FW_CFG() macro currently calls the
module-private helper function GetNamedFwCfgBoolean(). Replace the latter
with QemuFwCfgParseBool() from 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: <20200424075353.8489-4-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>