Match: Refactor min based unsigned SAT_MUL pattern by widen mul helper [NFC]

Match: Refactor min based unsigned SAT_MUL pattern by widen mul helper [NFC]

There are 3 kinds of widen_mul during the unsigned SAT_MUL pattern, aka
* widen_mul directly, like _3 w* _4
* convert and the widen_mul, like (uint64_t)_3 *w (uint64_t)_4
* convert and then mul, like (uint64_t)_3 * (uint64_t)_4

All of them will be referenced during different forms of unsigned
SAT_MUL pattern match, but actually we can wrap them into a helper
which present the "widening_mul" sematics.  With this helper, some
unnecessary pattern and duplicated code could be eliminated.

The below test suites are passed for this patch:
1. The rv64gcv fully regression tests.
2. The x86 bootstrap tests.
3. The x86 fully regression tests.

gcc/ChangeLog:

	* match.pd: Add usmul_widen_mult helper and referenced by
	min based unsigned SAT_MUL pattern.

Signed-off-by: Pan Li <pan2.li@intel.com>