ARM: Fix assertion caused by passing bitfield struct using ABIArgInfo::getExpandWithPadding

In cases where a struct must, according to the AAPCS, not be split between
general purpose and floating point registers, we use
ABIArgInfo::getExpandWithPadding to add the padding arguments. However,
ExpandWithPadding does not work if the struct contains bitfields, so we
instead must use ABIArgInfo::getDirect.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@208185 91177308-0d34-0410-b5e6-96231b3b80d8