AArch64: View the pseudo V registers as vectors

AArch64: View the pseudo V registers as vectors

When SVE is enabled, the V registers become pseudo registers based
on the Z registers.  They should look the same as they do when
there is no SVE.

The existing code viewed them as single value registers. Switch
this to a vector.

gdb/ChangeLog:

	* aarch64-tdep.c (aarch64_vnv_type): Use vector types.