[arm] Add MC asm header object file test cases.
[arm] Extract functions to emit .fpu directive.
[arm] Rename type name from AttributeItemType to AttributeItem.
[arm] Move ARMBuildAttrs to llvm namespace.
[arm] Compute the size of .ARM.attributes on demand.
[arm] Move AttrEmitter to ARMTargetStreamer.
[arm] Add .fpu, .cpu, .eabi_attribute to ARMAsmParser.