[PowerPC] Fix VSX registers in linux core files

[PowerPC] Fix VSX registers in linux core files

The functions used by the VSX regset to collect and supply registers
from core files where incorrect. This patch changes the regset to use
the standard regset collect/supply functions to fix this. The native
target is also changed to use the same regset.

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

	* ppc-linux-tdep.c (ppc_linux_vsxregset): New function.
	(ppc32_linux_vsxregmap): New global.
	(ppc32_linux_vsxregset): Initialize with ppc32_linux_vsxregmap,
	regcache_supply_regset, and regcache_collect_regset.
	* ppc-linux-tdep.h (ppc_linux_vsxregset): Declare.
	* ppc-linux-nat.c (supply_vsxregset, fill_vsxregset): Remove.
	(fetch_vsx_register, store_vsx_register): Remove.
	(fetch_vsx_registers): Add regno parameter. Get regset using
	ppc_linux_vsxregset. Use regset to supply registers.
	(store_vsx_registers): Add regno parameter. Get regset using
	ppc_linux_vsxregset. Use regset to collect registers.
	(fetch_register): Call fetch_vsx_registers instead of
	fetch_vsx_register.
	(store_register): Call store_vsx_registers instead of
	store_vsx_register.
	(fetch_ppc_registers): Call fetch_vsx_registers with -1 for the
	new regno parameter.
	(store_ppc_registers): Call store_vsx_registers with -1 for the
	new regno parameter.
	* rs6000-tdep.c (ppc_vsx_support_p, ppc_supply_vsxreget)
	(ppc_collect_vsxregset): Remove.

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

	* gdb.arch/powerpc-vsx-gcore.exp: New file.