gcc, Arm: Fix MVE move from GPR -> GPR

gcc, Arm: Fix MVE move from GPR -> GPR

This patch fixes the pattern mve_mov for the case where both MVE vectors are in
R registers and the move does not get optimized away.  I use the same approach
as we do for NEON, where we use four register moves.

gcc/ChangeLog:
2020-03-20  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* config/arm/mve.md (mve_mov<mode>): Fix R->R case.

gcc/testsuite/ChangeLog:
2020-03-20  Andre Vieira  <andre.simoesdiasvieira@arm.com>

	* gcc.target/arm/mve/intrinsics/mve_move_gpr_to_gpr.c: New test.