kas: Introduce UEFI Secure Boot feature

Add “meta-secure-core” layer which has the ssl certs/keys,
efitools-native and sbsigntool-native packages that will
be used in UEFI Secure Boot.
This feature is only enabled for baremetal use cases and
disabled for Virtualization, SystemReady IR ACS and
Distro installation use cases.

Signed-off-by: Amr Mohamed <amr.mohamed@arm.com>