arm: Call thumb1_gen_const_int from thumb1_movsi_insn
thumb1_movsi_insn used the same algorithm to build a constant in asm
than thumb1_gen_const_int_1 does in RTL. Since the previous patch added
support for asm generation in thumb1_gen_const_int_1, this patch calls
it from thumb1_movsi_insn to avoid duplication.
We need to introduce a new proxy function, thumb1_gen_const_int_print
to select the right template.
This patch also adds a new testcase as the updated alternative is only
used by thumb-1 processors that also support movt/movw.