target-ppc: Extend HWCAP2 bits for ISA 3.0

target-ppc: Extend HWCAP2 bits for ISA 3.0

This adds the HWCAP2 bit to detect if a linux user process is
running on an ISA 3.0 compliant cpu like POWER9. This can be
verified using a simple test program that prints the value in
the auxiliary vector for AT_HWCAP2 as shown below.

Before:
  $ qemu-ppc64le -cpu power8 test
  0x8c000000

  $ qemu-ppc64le -cpu power9 test
  0x8c000000

After:
  $ qemu-ppc64le -cpu power8 test
  0x8c000000

  $ qemu-ppc64le -cpu power9 test
  0x8c800000

Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>