Generilize mt76_get_of_eeprom_from_nvmem to use alternative cell name by
passing the cell name as an arg and expose it.

Rename it to mt76_get_of_data_from_nvmem to better reflect the now more
generic usage.

This is to permit driver to load additional cell, like precal cell.
Tested-by: Shiji Yang <yangshiji66@outlook.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>