linux-user/elfload.c: Support ARM HWCAP2 flags

The ARM kernel has chosen to spill into the HWCAP2 ELF feature bit flags
early, even though it hasn't yet exhausted all 32 bits of the HWCAP word.
Add support for setting this in the same way we do for HWCAP.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
