mmc: core: Add trace events to profile mmc suspend-resume

Add trace events to capture mmc suspend-resume latencies.
This would be useful to capture latencies for variety
of MMC/SD cards and decide on best possible runtime PM timeout.

Usage -
cd /sys/kernel/debug
echo 1 > tracing/events/mmc/mmc_resume_host/enable
echo 1 > tracing/events/mmc/mmc_suspend_host/enable
cat tracing/trace_pipe

Change-Id: Ic3a73753d55985c1c663cf2972cbed320e0fcfc3
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>