Convert CONFIG_ENV_SPI_* 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

Most of time these value are not needed, CONFIG_SF_DEFAULT
with same value is used, so I introduced CONFIG_USE_ENV_SPI_*
to force the associated value for the environment.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/configs/mscc_servalt_defconfig b/configs/mscc_servalt_defconfig
index a450f48..027aaa4 100644
--- a/configs/mscc_servalt_defconfig
+++ b/configs/mscc_servalt_defconfig
@@ -33,6 +33,10 @@
 CONFIG_DTB_RESELECT=y
 CONFIG_MULTI_DTB_FIT=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_USE_ENV_SPI_MAX_HZ=y
+CONFIG_ENV_SPI_MAX_HZ=0
+CONFIG_USE_ENV_SPI_MODE=y
+CONFIG_ENV_SPI_MODE=0
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_CLK=y
 CONFIG_DM_GPIO=y