init: Increase kernel command line buffer length

Increased cmdline buffer length from 1024 to 2048
in-order to accommodate AVB 2.0 boot arguments.

Change-Id: I26b3ad75c88d5cbf97766e86710f677e11a77df0
Signed-off-by: Phanindra Babu Pabba <pabba@codeaurora.org>