[AArch64] move extension information into tablgen (#90987)

Generate TargetParser extension information from tablegen. This includes FMV extension information. FMV only extensions are represented by a separate tablegen class.

Use MArchName/ArchKindEnumSpelling to avoid renamings.
Cases where there is simply a case difference are handled by
consistently uppercasing the AEK_ name in the emitted code.

Remove some Extensions which were not needed.
These had AEK entries but were never actually used for anything.
They are not present in Extensions[] data.