Blackfin: blackstamp: update spi flash settings

The latest blackstamp boards can only run the SPI flash at 15MHz before
they start to crap out, so lower the max speeds accordingly.  The new SPI
flash also has different sector requirements, so update the environment
sizes as well.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

include/configs/blackstamp.h

@@ -83,10 +83,9 @@
 #endif
 
 #define CONFIG_ENV_IS_IN_SPI_FLASH
-#define CONFIG_ENV_OFFSET	0x4000
+#define CONFIG_ENV_OFFSET	0x40000
 #define CONFIG_ENV_SIZE		0x2000
 #define CONFIG_ENV_SECT_SIZE	0x40000
-#define ENV_IS_EMBEDDED_CUSTOM
 
 /*
  * SDRAM settings & memory map
@@ -245,9 +244,9 @@
  * Serial Flash Infomation
  */
 #define CONFIG_BFIN_SPI
-/* For the M25P64 SCK Should be Kept < 20Mhz */
-#define CONFIG_ENV_SPI_MAX_HZ	20000000
-#define CONFIG_SF_DEFAULT_SPEED	20000000
+/* For the M25P64 SCK Should be Kept < 15Mhz */
+#define CONFIG_ENV_SPI_MAX_HZ	15000000
+#define CONFIG_SF_DEFAULT_SPEED	15000000
 #define CONFIG_SPI_FLASH
 #define CONFIG_SPI_FLASH_STMICRO