msm_serial_hs: IPC logs per device

Route the IPC logs of each UART port to
seperate file. This will make debugging easier
when two or more UART ports are enabled.

Change the debug level at runtime:
==================================
cd sys/devices/ctrl_num(eg:1234).uart
echo <log_level> > debug_mask

Logs of individual UART port:
=============================
sys/kernel/debug/ipc_logging/ctrl_num.uart/log_cont

Change-Id: I9292ff55e62d35045a5cb3304b1d75734eaa5389
Signed-off-by: Dilip Kota <dkota@codeaurora.org>