riscv: Add support for SPI on Kendryte K210

This enables configs necessary for using SPI. The environment is saved to
the very end of SPI flash. This is unlikely to be overwritten unless the
entire flash is reprogrammed.

This also supplies a default bootcommand. It loads an image and device tree
from the first partition of the MMC. This is a minimal/least effort
bootcmd, so suggestions (especially in the form of patches) are welcome. I
didn't set up distro boot because I think it is unlikely that any
general-purpose linux distros will ever be ported to this board.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Tested-by: Chrstopher Obbard <obbardc@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/sipeed_maix_bitm_defconfig b/configs/sipeed_maix_bitm_defconfig
index 459bf0d..210848c 100644
--- a/configs/sipeed_maix_bitm_defconfig
+++ b/configs/sipeed_maix_bitm_defconfig
@@ -1,8 +1,19 @@
 CONFIG_RISCV=y
+CONFIG_ENV_SIZE=0x1000
+CONFIG_ENV_OFFSET=0xfff000
+CONFIG_ENV_SECT_SIZE=0x1000
 CONFIG_TARGET_SIPEED_MAIX=y
 CONFIG_ARCH_RV64I=y
 CONFIG_STACK_SIZE=0x100000
+CONFIG_USE_BOOTCOMMAND=y
+CONFIG_BOOTCOMMAND="run k210_bootcmd"
+CONFIG_HUSH_PARSER=y
+CONFIG_MTDIDS_DEFAULT="nor0=spi3:0"
+CONFIG_MTDPARTS_DEFAULT="nor0:1M(u-boot),0x1000@0xfff000(env)"
 # CONFIG_NET is not set
 # CONFIG_INPUT is not set
+CONFIG_SF_DEFAULT_BUS=3
 # CONFIG_DM_ETH is not set
+CONFIG_FS_EXT4=y
+CONFIG_FS_FAT=y
 # CONFIG_EFI_LOADER is not set