ARM: 7981/1: add support for AT_HWCAP2 ELF auxv entry

This enables AT_HWCAP2 for ARM. The generic support for this
new ELF auxv entry was added in commit 2171364d (powerpc:
Add HWCAP2 aux entry)

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>