drivers/spi: fix flash writes at page boundaries

There was an assumption that all SPI controllers could
consume a full page of data to write. However, that
assumption doesn't hold when spi_crop_chunk() indicates
sizes smaller than page size. If the requested offset isn't
page aligned from the start then writes will fail corrupting
data since a page boundary isn't honored.

The spansion driver needed quite a bit more work to honor
the spi_crop_chunk() result. It now mimics the other
driver's code. Also, needed to add spi_crop_chunk() to
marvell/bg4cd SoC to make google/cosmos build. SPI obviously
doesn't work on that platform, but it fixes the build error.

Change-Id: I93e24a5a717adcee45a017c164bd960f4592ad50
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/17910
Tested-by: build bot (Jenkins)
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/drivers/spi/atmel.c b/src/drivers/spi/atmel.c
index feb1a6d..39cc95e 100644
--- a/src/drivers/spi/atmel.c
+++ b/src/drivers/spi/atmel.c
@@ -121,9 +121,9 @@
 	u8 cmd[4];
 
 	page_size = 1 << stm->params->l2_page_size;
-	byte_addr = offset % page_size;
 
 	for (actual = 0; actual < len; actual += chunk_len) {
+		byte_addr = offset % page_size;
 		chunk_len = min(len - actual, page_size - byte_addr);
 		chunk_len = spi_crop_chunk(sizeof(cmd), chunk_len);
 
@@ -155,7 +155,6 @@
 			goto out;
 
 		offset += chunk_len;
-		byte_addr = 0;
 	}
 
 #if CONFIG_DEBUG_SPI_FLASH