[PowerPC] Consolidate linux vector regset sizes

[PowerPC] Consolidate linux vector regset sizes

This patch defines constants for the sizes of the two vector
regsets (vector-scalar registers and regular vector registers).

The native, gdbserver and core file targets are changed to use these
constants.

The Linux ptrace calls return (or read) a smaller regset than the one
found in core files for vector registers, because ptrace uses a single
4-byte quantity for vrsave at the end of the regset, while the
core-file regset uses a full 16-byte field for vrsave. For simplicity,
the larger size is used in both cases, and so a buffer with 12 unused
additional bytes is passed to ptrace in the native target.

gdb/ChangeLog:
2018-05-22  Pedro Franco de Carvalho  <pedromfc@linux.vnet.ibm.com>

	* arch/ppc-linux-common.h (PPC_LINUX_SIZEOF_VRREGSET)
	(PPC_LINUX_SIZEOF_VSXREGSET): Define.
	* ppc-linux-nat.c (SIZEOF_VSXREGS, SIZEOF_VRREGS): Remove.
	(gdb_vrregset_t): Change array type size to
	PPC_LINUX_SIZEOF_VRREGSET.
	(gdb_vsxregset_t): Change array type size to
	PPC_LINUX_SIZEOF_VSXREGSET.
	* ppc-linux-tdep.c (ppc_linux_iterate_over_regset_sections):
	Change integer literals to PPC_LINUX_SIZEOF_VRREGSET and
	PPC_LINUX_SIZEOF_VSXREGSET.

gdb/gdbserver/ChangeLog:
2018-05-22  Pedro Franco de Carvalho  <pedromfc@linux.vnet.ibm.com>

	* linux-ppc-low.c (SIZEOF_VSXREGS, SIZEOF_VRREGS): Remove.
	(ppc_arch_setup): Change SIZEOF_VRREGS and SIZEOF_VSXREGS to
	PPC_LINUX_SIZEOF_VRREGSET and PPC_LINUX_SIZEOF_VSXREGSET.