linux-user/elfload.c: Fix A64 code which was incorrectly acting like A32

linux-user/elfload.c: Fix A64 code which was incorrectly acting like A32

The ARM target-specific code in elfload.c was incorrectly allowing
the 64-bit ARM target to use most of the existing 32-bit definitions:
most noticably this meant that our HWCAP bits passed to the guest
were wrong, and register handling when dumping core was totally
broken. Fix this by properly separating the 64 and 32 bit code,
since they have more differences than similarities.

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