efi/arm64: ignore dtb= when UEFI SecureBoot is enabled

efi/arm64: ignore dtb= when UEFI SecureBoot is enabled

Loading unauthenticated FDT blobs directly from storage is a security hazard,
so this should only be allowed when running with UEFI Secure Boot disabled.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
(cherry picked from commit 345c736edd07b657a8c48190baed2719b85d0938)
Signed-off-by: Mark Brown <broonie@linaro.org>