[PowerPC] Don't zero-initialize vector register buffers

[PowerPC] Don't zero-initialize vector register buffers

Now that linux-tdep.c already zero-initializes the buffer used for
generating core file notes, there is no need to do this in the linux
collect functions for the vector regset.  The memsets in gdbserver were
not useful to begin with.

gdb/ChangeLog:
2018-10-26  Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* ppc-linux-tdep.c (ppc_linux_collect_vrregset): Remove.
	(ppc32_le_linux_vrregset, ppc32_be_linux_vrregset): Replace
	ppc_linux_collect_vrregset by regcache_collect_regset.

gdb/gdbserver/ChangeLog:
2018-10-26  Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* linux-ppc-low.c (ppc_fill_vrregset): Remove memset calls.