Documentation: Add Arm Ltd to kernel-enforcement-statement.rst

Adding a couple of names on behalf of Arm Ltd.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>