[lra] reorder operations in lra_update_fp2sp_elimination [PR120424]

[lra] reorder operations in lra_update_fp2sp_elimination [PR120424]

The various recent additions to lra_update_fp2sp_elimination rendered
it somewhat confusing, with intermixed groups of statements pertaining
to three different major actions: disabling the elimination,
recomputing live ranges, and spilling uses of the frame pointer.
Reorder them for readability.

for  gcc/ChangeLog

	PR rtl-optimization/120424
	* lra-eliminations.cc (lra_update_fp2sp_elimination): Reorder
	and regroup related statements.