OvmfPkg: Build and use the UEFI shell by default

OvmfPkg: Build and use the UEFI shell by default

Previously OVMF included the older EFI shell binary when building.

Now we will build and use the UEFI shell (ShellPkg) instead.

v2:
 * Don't bother building UEFI shell when USE_OLD_SHELL is defined
 * Fix errors in OvmfPkgIa32X64.fdf

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14600 6f19259b-4bc3-4df7-8a09-765794883524