amdgcn: Disallow unsupported permute on RDNA devices

The RDNA architecture has limited support for permute operations.  This should
allow use of the permutations that do work, and fall back to linear code for
other cases.

gcc/ChangeLog:

	* config/gcn/gcn-valu.md
	(vec_extract<V_MOV:mode><V_MOV_ALT:mode>): Add conditions for RDNA.
	* config/gcn/gcn.cc (gcn_vectorize_vec_perm_const): Check permutation
	details are supported on RDNA devices.