* dwarf2expr.h (struct dwarf_expr_context): Remove extra arguments

	* dwarf2expr.h (struct dwarf_expr_context): Remove extra arguments
	to read_reg and update its comment.  Remove regnum member.
	* dwarf2expr.c (execute_stack_op): Remove memaddr and expr_lval.
	Don't call read_reg when setting in_reg.  Call read_reg to get
	the frame base if it's in a register.  Return the register number
	on the stack instead of in the context.  Remove extra arguments
	to read_reg.
	* dwarf2loc.c (dwarf_expr_read_reg): Remove extra arguments.
	(dwarf2_evaluate_loc_desc): Call value_from_register.  Expect
	the register number on the expression stack.
	(needs_frame_read_reg): Remove extra arguments.