Revert "Remove loglevel from default kernel boot arguments"

This reverts commit 01e049d704cfba97192efeed6afabd71cf7ca130.

It seems default loglevel cannot be set in kernel .config.

qiboot/src/cpu/s3c2410/gta01.c

@@ -263,6 +263,7 @@ const struct board_api board_api_gta01 = {
 				 "0x00200000(kernel),"
 				 "0x000a0000(splash),"
 				 "0x03d1c000(rootfs) "
+			       "loglevel=4 "
 			       "console=tty0 "
 			       "console=ttySAC0,115200 "
 			       "init=/sbin/init "

qiboot/src/cpu/s3c2442/gta02.c

@@ -690,7 +690,8 @@ const struct board_api board_api_gta02 = {
 	.get_ui_keys = get_ui_keys_gta02,
 	.get_ui_debug = get_ui_debug_gta02,
 	.set_ui_indication = set_ui_indication_gta02,
-	.commandline_board = "console=tty0 "
+	.commandline_board = "loglevel=4 "
+				      "console=tty0 "
 				      "console=ttySAC2,115200 "
 				      "init=/sbin/init "
 				      "ro ",

qiboot/src/cpu/s3c6410/om_3d7k-steppingstone.c

@@ -88,6 +88,7 @@ const struct board_api board_api_om_3d7k = {
 	.commandline_board = "console=tty0 "
 			     "console=ttySAC3,115200 "
 			     "init=/sbin/init "
+			     "loglevel=8 "
 			     "rootdelay=1 no_console_suspend "
 			     "ro ",
 	.commandline_board_debug =  " loglevel=8",