Update naming for xcvmem instructions

Created by: ChunyuLiao

fix issue71 https://github.com/openhwgroup/corev-llvm-project/issues/71

spec: https://github.com/openhwgroup/cv32e40p/pull/844/files cv.l* rD, Imm(rs1!) by cv.l* rD, (rs1), imm and resp. cv.s* rs2, Imm(rs1!) by cv.s* rs2, (rs1), imm cv.l* rD, rs2(rs1!) by cv.l* rD, (rs1), rs2 and resp. cv.s* rs2, rs3(rs1!) by cv.s* rs2, (rs1), rs3