mhi: core: add sysfs hook to modify IPC log levels

Add option to allow modification of IPC log debug levels
from sysfs.

CRs-Fixed: 2509935
Change-Id: I002d6da2e7dd2e0357672f16290ef43be798bf89
Acked-by: Bhaumik Vasav Bhatt <bbhatt@qti.qualcomm.com>
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>