binfmt_elf: add ELF_HWCAP2 to compat auxv entries

Add ELF_HWCAP2 to the set of auxv entries that is passed to
a 32-bit ELF program running in 32-bit compat mode under a
64-bit kernel.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>