msm: smem_log: Use sched_clock() for SMEM Log Timestamp

Most targets use a 32.768KHz RTC clock for the SMEM Log timestamp.
However, this is not available for 8974, so we will switch to using the
sched_clock() which also has the advantage of being able to correlate
APPS SMEM Log items with the kernel log.

CRs-Fixed: 347156
Change-Id: Ia2010a7841bba9425beb737389e45e6b78cb1d89
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>