aarch64/gdbserver: fix floating point registers display

aarch64/gdbserver: fix floating point registers display

When using aarch64 gdb with gdbserver, floating point registers are
not correctly displayed, as below:
  (gdb) info registers fpsr fpcr
  fpsr           <unavailable>
  fpcr           <unavailable>

To fix these problems, the missing fpsr and fpcr registers are added
when floating point registers are read/write
Add test for aarch64 floating point
PR server/17457

gdb/gdbserver/

    PR server/17457
    * linux-aarch64-low.c (AARCH64_FPSR_REGNO): New define.
    (AARCH64_FPCR_REGNO): Likewise.
    (AARCH64_NUM_REGS): Update to include fpsr/fpcr registers.
    (aarch64_fill_fpregset): Add missing fpsr/fpcr registers.
    (aarch64_store_fpregset): Likewise.

gdb/testsuite/

    PR server/17457
    * gdb.arch/aarch64-fp.c: New file.
    * gdb.arch/aarch64-fp.exp: New file.

Signed-off-by: Catalin Udma <catalin.udma@freescale.com>