Fix costs of x86 move instructions at -Os

Fix costs of x86 move instructions at -Os

This patch fixes problem with size costs declaring all moves to have equal size
(which was caught by the sanity check I tried in prologue move cost hook).
Costs are relative to reg-reg move which is two. Coincidentally it is also size
of the encoding, so the costs should represent typical size of move
instruction.

The patch reduces cc1plus text size 26391115->26205707 (0.7%) and similar changes
also happens to other binaries build during bootstrap.

Bootsrapped/regtested x86_64-linux, plan to commit it tomorrow if there
are no complains

There are other targets that define some load/store costs to be 2 that probably
should be fixed too, but they are mostly very old ones and I don't have way of
benchmarking them.

	* config/i386/x86-tune-costs.h (ix86_size_cost): Fix sizes of move
	instructions