With features AVB / dm-verity enabled, cmdline content is about to
exceed previous maximum 2048 bytes. Increase the cmdline buffer size
(COMMAND_LINE_SIZE) to 4096 bytes for other features to use.
Change-Id: I73baf92e5dce1a341d523b1a976d387e794b3998
Signed-off-by: Tao Huang <huangtao@rock-chips.com>