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/lx2160aqds_tfa_defconfig b/configs/lx2160aqds_tfa_defconfig
index 32ea3cb..3b8dde9 100644
--- a/configs/lx2160aqds_tfa_defconfig
+++ b/configs/lx2160aqds_tfa_defconfig
@@ -37,6 +37,7 @@
 CONFIG_BOARD_EARLY_INIT_R=y
 CONFIG_MISC_INIT_R=y
 CONFIG_RESET_PHY_R=y
+CONFIG_SYS_MAXARGS=64
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_EEPROM=y
 CONFIG_SYS_EEPROM_PAGE_WRITE_BITS=3