SecurityPkg: don't require PK to be self-signed by default

SecurityPkg: don't require PK to be self-signed by default

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2506

Change the default value of PcdRequireSelfSignedPk to FALSE in
accordance with UEFI spec, which states that PK need not be
self-signed when enrolling in setup mode.

Note that this relaxes the legacy behavior, which required the PK to
be self-signed in this case.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Signed-off-by: Jan Bobek <jbobek@nvidia.com>
Reviewed-by: Sean Brogan <sean.brogan@microsoft.com>
Acked-by: Jiewen Yao <jiewen.yao@intel.com>