[ARM] Fix encoding of APSR in CLRM instruction

The APSR is encoded by setting bit 15 in the register list of the CLRM
instruction (cf. https://static.docs.arm.com/ddi0553/bh/DDI0553B_h_armv8m_arm.pdf).

Differential Revision: https://reviews.llvm.org/D65873

llvm-svn: 368711