Documentation: nvmem: document cell tables and lookup entries

Document the new nvmem kernel APIs.

Signed-off-by: Bartosz Golaszewski <[e-mail]>
Signed-off-by: Srinivas Kandagatla <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/nvmem/nvmem.txt

···
 It is mandatory that the NVMEM provider has a regmap associated with its
 struct device. Failure to do would return error code from nvmem_register().
 
+Users of board files can define and register nvmem cells using the
+nvmem_cell_table struct:
+
+static struct nvmem_cell_info foo_nvmem_cells[] = {
+	{
+		.name		= "macaddr",
+		.offset		= 0x7f00,
+		.bytes		= ETH_ALEN,
+	}
+};
+
+static struct nvmem_cell_table foo_nvmem_cell_table = {
+	.nvmem_name		= "i2c-eeprom",
+	.cells			= foo_nvmem_cells,
+	.ncells			= ARRAY_SIZE(foo_nvmem_cells),
+};
+
+nvmem_add_cell_table(&foo_nvmem_cell_table);
+
+Additionally it is possible to create nvmem cell lookup entries and register
+them with the nvmem framework from machine code as shown in the example below:
+
+static struct nvmem_cell_lookup foo_nvmem_lookup = {
+	.nvmem_name		= "i2c-eeprom",
+	.cell_name		= "macaddr",
+	.dev_id			= "foo_mac.0",
+	.con_id			= "mac-address",
+};
+
+nvmem_add_cell_lookups(&foo_nvmem_lookup, 1);
+
 NVMEM Consumers
 +++++++++++++++