arm64: 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.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>