[RISCV] Mark C.EBREAK instruction as having side effects

[RISCV] Mark C.EBREAK instruction as having side effects

C.EBREAK was defined with hasSideEffects = 0, which is incorrect and
inconsistent with the non-compressed instruction form. This patch corrects
this oversight.

This wouldn't cause codegen issues, as compressed instructions are only ever
generated by converting the non-compressed form as an MCInst. But having
correct flags is still worthwhile.

Differential Revision: https://reviews.llvm.org/D54256
Patch by Luís Marques.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346959 91177308-0d34-0410-b5e6-96231b3b80d8