add autogeneration for mac and msu builtins

* gcc/config/riscv/corev.md: update the builtins patterns.
*
gcc/testsuite/gcc.target/riscv/cv-march-xcvmac-test-autogeneration-mac.c:
test for autogeneration.
*
gcc/testsuite/gcc.target/riscv/cv-march-xcvmac-test-autogeneration-msu.c:
Likewise.