elf: Add powerpc specific core note sections

This patch adds twelve ELF core note sections for powerpc
architecture for various registers and register sets which
need to be accessed from ptrace interface and then gdb.
These additions include special purpose registers like TAR,
PPR, DSCR, TM running and checkpointed state for various
register sets, EBB related register set, performance monitor
register set etc. Addition of these new ELF core note
sections extends the existing ELF ABI on powerpc arch without
affecting it in any manner.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>