nvmem: Remove unused nvmem cell table support

Board files are deprecated by DT, and the last user of
nvmem_add_cell_table() was removed by commit 2af4fcc0 ("ARM:
davinci: remove unused board support") in v6.3.  Hence remove all
support for nvmem cell tables, and update the documentation.

Device drivers can still register a single cell using
nvmem_add_one_cell() (which was not documented before).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
Link: https://lore.kernel.org/r/20250509122452.11827-2-srini@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>