arm64: Use core efi=debug instead of uefi_debug command line parameter

Now that we have an efi=debug command line option in the core code, use
this instead of the arm64-specific uefi_debug option.

Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Mark Salter <msalter@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>