Ensure we get a valid gdbarch for arc_scan_prologue. Tidy up minor glitches elsewhere.

2013-03-13  Jeremy Bennett <jeremy.bennett@embecosm.com>

	* arc-tdep.c (arc_scan_prologue): Add GDBARCH parameter. No need
	to get pc_regnum.
	(arc_skip_trampoline_code): Return PC as result.
	(arc_print_float_info): Correct type of parameters.