tcg: Add tcg_gen_gvec_dup_imm

tcg: Add tcg_gen_gvec_dup_imm

Add a version of tcg_gen_dup_* that takes both immediate and
a vector element size operand.  This will replace the set of
tcg_gen_gvec_dup{8,16,32,64}i functions that encode the element
size within the function name.

Reviewed-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>