CV32E40Pv2 MAC pseudo-instructions

Created by: NandniJamnadas

This is where `cv.mul* rD, rs1, rs2` is `cv.mul*n rD, rs1, rs2, 0`.

* include/opcode/riscv-opc.h: Removed corresponding MATCH and MASK macros.
* opcodes/riscv-opc.c: Implemented:
	* MASK_CV_MAC_UIMM5 macro which masks 0 for Is3 operand
	* infrastructure for CORE-V MAC alias instructions.
* gas/testsuite/gas/riscv/cv-mac-mulhhs.d: Updated tests.
* gas/testsuite/gas/riscv/cv-mac-mulhhs.s: Likewise.
* gas/testsuite/gas/riscv/cv-mac-mulhhu.d: Likewise.
* gas/testsuite/gas/riscv/cv-mac-mulhhu.s: Likewise.
* gas/testsuite/gas/riscv/cv-mac-muls.d: Likewise.
* gas/testsuite/gas/riscv/cv-mac-muls.s: Likewise.
* gas/testsuite/gas/riscv/cv-mac-mulu.d: Likewise.
* gas/testsuite/gas/riscv/cv-mac-mulu.s: Likewise.