efi/libstub/arm/arm64: Disable debug prints on 'quiet' cmdline arg

efi/libstub/arm/arm64: Disable debug prints on 'quiet' cmdline arg

The EFI stub currently prints a number of diagnostic messages that do
not carry a lot of information. Since these prints are not controlled
by 'loglevel' or other command line parameters, and since they appear on
the EFI framebuffer as well (if enabled), it would be nice if we could
turn them off.

So let's add support for the 'quiet' command line parameter in the stub,
and disable the non-error prints if it is passed.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bhe@redhat.com
Cc: bhsharma@redhat.com
Cc: bp@alien8.de
Cc: eugene@hp.com
Cc: evgeny.kalugin@intel.com
Cc: jhugo@codeaurora.org
Cc: leif.lindholm@linaro.org
Cc: linux-efi@vger.kernel.org
Cc: roy.franz@cavium.com
Cc: rruigrok@codeaurora.org
Link: http://lkml.kernel.org/r/20170404160910.28115-2-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>