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_stratix10_atf_defconfig b/configs/socfpga_stratix10_atf_defconfig
index 6d2f473..50bab70 100644
--- a/configs/socfpga_stratix10_atf_defconfig
+++ b/configs/socfpga_stratix10_atf_defconfig
@@ -32,6 +32,7 @@
 CONFIG_SPL_ATF_NO_PLATFORM_PARAM=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="SOCFPGA_STRATIX10 # "
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_MEMTEST=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y