Convert CONFIG_SYS_MAXARGS to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MAXARGS

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/socfpga_de0_nano_soc_defconfig b/configs/socfpga_de0_nano_soc_defconfig
index 2e5bd80..e45e3db 100644
--- a/configs/socfpga_de0_nano_soc_defconfig
+++ b/configs/socfpga_de0_nano_soc_defconfig
@@ -21,6 +21,7 @@
 # CONFIG_SPL_RAW_IMAGE_SUPPORT is not set
 CONFIG_SPL_SPI_LOAD=y
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x40000
+CONFIG_SYS_MAXARGS=32
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_DFU=y