Convert CONFIG_ENV_SPI_BUS et al to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_SPI_BUS
   CONFIG_ENV_SPI_CS
   CONFIG_ENV_SPI_MAX_HZ
   CONFIG_ENV_SPI_MODE

As part of this, we use Kconfig to provide the defaults now that were
done in include/spi_flash.h.  We also in some cases change from using
CONFIG_ENV_SPI_FOO to CONFIG_SF_DEFAULT_FOO as those were the values in
use anyhow as ENV was not enabled.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mtd/spi/Kconfig b/drivers/mtd/spi/Kconfig
index 408a53f..0969c03 100644
--- a/drivers/mtd/spi/Kconfig
+++ b/drivers/mtd/spi/Kconfig
@@ -57,7 +57,7 @@
 config SF_DEFAULT_MODE
 	hex "SPI Flash default mode (see include/spi.h)"
 	depends on SPI_FLASH || DM_SPI_FLASH
-	default 0
+	default 0x0
 	help
 	  The default mode may be provided by the platform
 	  to handle the common case when only a single serial