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/mt7623n_bpir2_defconfig b/configs/mt7623n_bpir2_defconfig
index 677e192..e2d68b9 100644
--- a/configs/mt7623n_bpir2_defconfig
+++ b/configs/mt7623n_bpir2_defconfig
@@ -17,6 +17,7 @@
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot> "
+CONFIG_SYS_MAXARGS=8
 CONFIG_CMD_BOOTMENU=y
 # CONFIG_CMD_ELF is not set
 # CONFIG_CMD_XIMG is not set