doc: Add more alias option and reorder Intel CPU -march documentation

doc: Add more alias option and reorder Intel CPU -march documentation

This patch is backported from GCC15 with some tweaks.

Since r15-3539, there are requests coming in to add other alias option
documentation. This patch will add all of them, including corei7, corei7-avx,
core-avx-i, core-avx2, atom and slm.

Also in the patch, I reordered that part of documentation, currently all
the CPUs/products are just all over the place. I regrouped them by
date-to-now products (since the very first CPU to latest Panther Lake), P-core
(since the clients become hybrid cores, starting from Sapphire Rapids) and
E-core (since Bonnell). In GCC14 and eariler GCC, Xeon Phi CPUs are still
there, I put them after E-core CPUs.

And in the patch, I refined the product names in documentation.

gcc/ChangeLog:

	* doc/invoke.texi: Add corei7, corei7-avx, core-avx-i,
	core-avx2, atom, and slm. Reorder the -march documentation by
	splitting them into date-to-now products, P-core, E-core and
	Xeon Phi. Refine the product names in documentation.