OvmfPkg: Add VariableFlashInfoLib

OvmfPkg: Add VariableFlashInfoLib

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3479

Adds an instance of VariableFlashInfoLib to the platform build as
it is a new library class introduced in MdeModulePkg.

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien@xen.org>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Peter Grehan <grehan@freebsd.org>
Cc: Rebecca Cran <rebecca@bsdio.com>
Cc: Sebastien Boeuf <sebastien.boeuf@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Rebecca Cran <rebecca@bsdio.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>