arm/efi: Remove forbidden values from the PE/COFF header

Bring the PE/COFF header in line with the PE/COFF spec, by setting
NumberOfSymbols to 0, and removing the section alignment flags.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170818194947.19347-9-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>