[APX EGPR] Add register and memory constraints that disallow EGPR

[APX EGPR] Add register and memory constraints that disallow EGPR

For APX, as we extended the GENERAL_REG_CLASS, new constraints are
needed to restrict insns that cannot adopt EGPR either in its reg or
memory operands. We added a series of constraints for general/backend
ones that related to GPR usage. All of them are prefixed with "j" to
indicate the constraints does not allow EGPR.

gcc/ChangeLog:

	* config/i386/constraints.md (jr): New register constraint
	that prohibits EGPR.
	(jR): Constraint that force usage of EGPR.
	(jm): New memory constraint that prohibits EGPR.
	(ja): Likewise for Bm constraint.
	(jb): Likewise for Tv constraint.
	(j<): New auto-dec memory constraint that prohibits EGPR.
	(j>): Likewise for ">" constraint.
	(jo): Likewise for "o" constraint.
	(jv): Likewise for "V" constraint.
	(jp): Likewise for "p" constraint.
	* config/i386/i386.h (enum reg_class): Add new reg class
	GENERAL_GPR16.

Co-authored-by: Hongyu Wang <hongyu.wang@intel.com>
Co-authored-by: Hongtao Liu <hongtao.liu@intel.com>