nvmem: core: remove nvmem_sysfs_get_groups()

Now that we are using is_bin_visible callback, we do not need
nvmem_sysfs_get_groups() anymore so move all the relevant data-structures
and code to core.c

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200325131951.31887-3-srinivas.kandagatla@linaro.org


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