slim_msm_ngd: Add IPC logging support

Add IPC logging support for improved debugging
per device, and in memory to avoid using kernel
dmesg logs.

Logs are captured in four levels.
1) error level ---> All fatal errors are logged
2) warn level  ---> error level logs +
Warning messages are logged
3) Info level  ---> Error level +
warn level + the required information
for debugging is logged
4) Debug level ----> error level + warn level +
info level logs + extra information
for debugging are logged

Procedure to change the debug level at runtime:
==============================================
cd sys/devices/ctrl_num(eg:1234).slim
echo <log_level> > debug_mask

Procedure to collect the logs at run time:
=========================================
adb shell cat sys/kernel/debug/ipc_logging/ctrl_num.slim/log_cont
|tee slimbus.txt

CRs-Fixed: 645838
Change-Id: If183533472ee61b2d8cf458d228dd4ae2124dd37
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>