[AArch64] Migrate from SearchableTable to GenericTable/Enum

SearchableTable is the legacy version that does not appear to be
well documented. Not sure if the plan was to delete it eventually.

We can eventually use the PrimaryKey feature of GenericTable to
remove one of the SearchIndex declarations. This will sort the
generated table by the primary key and remove the separately
generated indexing table to reduce .rodata size.

This patch is just the mechanical migration. The size savings will
be done in follow ups.

Author: topperc