OvmfPkg: resolve BcfgCommandLib class for ShellPkg/.../Shell.inf

OvmfPkg: resolve BcfgCommandLib class for ShellPkg/.../Shell.inf

SVN r16092 ('ShellPkg: Add a new library for "bcfg" command') introduced a
new library class (and an instance for it) called BcfgCommandLib.

SVN r16093 ('ShellPkg: Use the new library for "bcfg" command') rebased
ShellPkg to the new library, introducing a new [LibraryClasses]
dependency.

Library classes must be resolved to library instances in client platform
descriptions (DSC's). Since OVMF is a client platform, import the same
library resolution as seen in "ShellPkg/ShellPkg.dsc" (added in SVN
r16092).

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16095 6f19259b-4bc3-4df7-8a09-765794883524