This commit adds the eabi_attribute, cpu, and fpu directives
support to the ARM assembly parser. Besides, this commit
also moves switchVendor(), emitAttribute(),
emitTextAttribute(), emitFPU() to ARMTargetStreamer.
It has been verified that the output binaries of the changed
test case remain unchanged.
For not breaking the existing test cases, I have to add FeatureD16 to cortex-r5 subtarget. Although this is the default behavior of GCC, however, I can't find any document stating cortex-r5 has only d0-d15. Should I change the test case instead?