mtd: spi-nor: Add support for sst25wf020a

It is a 256KiB flash with 4 KiB erase sectors
and 64KiB overlay blocks.

This is the one available on Hardkernel's Odroid U3 shield.
Signed-off-by: Alexis Ballier <aballier@gentoo.org>
[Brian: seems like this does NOT require the usual SST_WRITE hacks]
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/spi-nor/spi-nor.c

@@ -634,6 +634,7 @@ static const struct flash_info spi_nor_ids[] = {
 	{ "sst25wf512",  INFO(0xbf2501, 0, 64 * 1024,  1, SECT_4K | SST_WRITE) },
 	{ "sst25wf010",  INFO(0xbf2502, 0, 64 * 1024,  2, SECT_4K | SST_WRITE) },
 	{ "sst25wf020",  INFO(0xbf2503, 0, 64 * 1024,  4, SECT_4K | SST_WRITE) },
+	{ "sst25wf020a", INFO(0x621612, 0, 64 * 1024,  4, SECT_4K) },
 	{ "sst25wf040",  INFO(0xbf2504, 0, 64 * 1024,  8, SECT_4K | SST_WRITE) },
 	{ "sst25wf080",  INFO(0xbf2505, 0, 64 * 1024, 16, SECT_4K | SST_WRITE) },