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/turris_omnia_defconfig b/configs/turris_omnia_defconfig
index da94ca7..b8b01e2 100644
--- a/configs/turris_omnia_defconfig
+++ b/configs/turris_omnia_defconfig
@@ -39,6 +39,7 @@
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_I2C=y
+CONFIG_SYS_MAXARGS=32
 CONFIG_CMD_MEMTEST=y
 CONFIG_SYS_ALT_MEMTEST=y
 CONFIG_CMD_SHA1SUM=y