Improve the dup pattern to prefer vector registers.  When doing a dup
after a load, the register allocator thinks the costs are identical
and chooses an integer load.  However a dup from an integer register
includes an int->fp transfer which is not modelled.  Adding a '?' to
the integer variant means the cost is increased slightly so we prefer
using a vector register.  This improves the following example:

#include <arm_neon.h>
void f(unsigned *a, uint32x4_t *b)
{
  b[0] = vdupq_n_u32(a[1]);
  b[1] = vdupq_n_u32(a[2]);
}

to:
        ldr     s0, [x0, 4]
        dup     v0.4s, v0.s[0]
        str     q0, [x1]
        ldr     s0, [x0, 8]
        dup     v0.4s, v0.s[0]
        str     q0, [x1, 16]
        ret

    gcc/
	* config/aarch64/aarch64-simd.md (aarch64_simd_dup):
	Swap alternatives, make integer dup more expensive.

From-SVN: r249443