mtd: spi-nor: Add support for Cypress cy15x104q

The Cypress cy15b104q and cy15v104q are 4Mbit serial SPI F-RAM devices.
Add support for them to the spi-nor driver.

The actual Device ID of this chip is 7f 7f 7f 7f 7f 7f c2 2c 04. That is
six times the continuation code 7f followed by c2 for Ramtron.
Unfortunately the chip sends the Device ID in reversed order, so the
continuation code is not at the beginning, but instead at the end. Even
more unfortunate is that when reading further the chip sends more 7f
codes which means we are not even able to count the continuation codes.
We can only hope that this reversed Device ID will never match any other
devices ID.

Collisions are improbable as of now, the solution from above is good
enough. In case of future collisions one can introduce an INFO9 macro,
with the downsize that struct flash_info would grow and we have lots of
flashes. A more elegant solution would be to introduce dedicated
flash ID tables for each bank in JESP106BA.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
[tudor.ambarus@microchip.com: amend commit description with possible
future solutions in case collisions occur.]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>

drivers/mtd/spi-nor/spansion.c

@@ -102,6 +102,8 @@ static const struct flash_info spansion_parts[] = {
 	{ "s25fl256l",  INFO(0x016019,      0,  64 * 1024, 512,
 			     SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ |
 			     SPI_NOR_4B_OPCODES) },
+	{ "cy15x104q",  INFO6(0x042cc2, 0x7f7f7f, 512 * 1024, 1,
+			      SPI_NOR_NO_ERASE) },
 };
 
 static void spansion_post_sfdp_fixups(struct spi_nor *nor)