Rearrange ppc_size_one_stub and correct _notoc stub examples

Rearrange ppc_size_one_stub and correct _notoc stub examples

This patch rearranges ppc_size_one_stub to make it a little easier to
compare against ppc_build_one_stub, and makes a few other random
changes that might help for future maintenance.  There should be no
functional changes here.

The patch also fixes code examples in comments.  A couple of "ori"
instructions lacked the source register operand, and "@high" is the
correct reloc modifier to use in a sequence building a 64-bit value.
(@hi reports overflow of a 32-bit signed value.)

	* elf64-ppc.c: Correct _notoc stub comments.
	(ppc_build_one_stub): Simplify output of branch for notoc
	long branch stub.  Don't include label offset of 8 bytes in
	"off" calculation for notoc plt stub.  Don't emit insns to get pc.
	(build_offset): Emit insns to get pc here instead.
	(size_offset): Add 4 extra insns.
	(plt_stub_size): Adjust for "off" and size_offset changes.
	(ppc_size_one_stub): Rearrange code into a switch, duplicating
	some to better match ppc_build_one_stub.