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_de10_standard_defconfig b/configs/socfpga_de10_standard_defconfig
index 91bd498..0a2a190 100644
--- a/configs/socfpga_de10_standard_defconfig
+++ b/configs/socfpga_de10_standard_defconfig
@@ -20,6 +20,7 @@
 CONFIG_CLOCKS=y
 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