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_arria10_defconfig b/configs/socfpga_arria10_defconfig
index 1be9a2d..903d885 100644
--- a/configs/socfpga_arria10_defconfig
+++ b/configs/socfpga_arria10_defconfig
@@ -26,6 +26,7 @@
 CONFIG_CLOCKS=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_FPGA=y
+CONFIG_SYS_MAXARGS=32
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 # CONFIG_CMD_FLASH is not set