ARM: dts: msm: Add kernel cmdline to increase the dmesg buffer size

By default, the size of the dmesg buffer is 128K. Due to additional
logging from drivers, the buffer overflows and the initial
set of logs are lost. Since these logs are critical for performance
measurements, increase the buffer size to 256K to preserve the logs.

Change-Id: I3645597754aab7dec9b2de22b4d6d14b88c994a3