OMAP: omap_device: optionally auto-adjust device activate/deactivate latencies

OMAP: omap_device: optionally auto-adjust device activate/deactivate latencies

First, this patch adds new worst-case latency values to the
omap_device_pm_latency struct.  Here the worst-case measured latencies
for the activate and deactivate hooks are stored.

In addition, add an option to auto-adjust the latency values used for
device activate/deactivate.

By setting a new 'OMAP_DEVICE_LATENCY_AUTO_ADJUST' flag in the
omap_device_pm_latency struct, the omap_device layer automatically
adjusts the activate/deactivate latencies to the worst-case measured
values.

Anytime a new worst-case value is found, it is printed to the console.
Here is an example log during boot using UART2 s an example.  After
boot, the OPP is manually changed to the 125MHz OPP:

[...]
Freeing init memory: 128K
omap_device: serial8250.2: new worst case deactivate latency 0: 30517
omap_device: serial8250.2: new worst case activate latency 0: 30517
omap_device: serial8250.2: new worst case activate latency 0: 218139648
omap_device: serial8250.2: new worst case deactivate latency 0: 61035
omap_device: serial8250.2: new worst case activate latency 0: 278076171
omap_device: serial8250.2: new worst case activate latency 0: 298614501
omap_device: serial8250.2: new worst case activate latency 0: 327331542

/ # echo 125000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed

omap_device: serial8250.2: new worst case deactivate latency 0: 91552

Motivation: this can be used as a technique to automatically determine
the worst case latency values.  The current method of printing a
warning on every violation is too noisy to actually interact the
console in order to set low OPP to discover latencies.

Another motivation for this patch is that the activate/deactivate
latenices can vary depending on the idlemode of the device.  While
working on the UARTs, I noticed that when using no-idle, the activate
latencies were as high as several hundred msecs as shown above.  When
the UARTs are in smart-idle, the max latency is well under 100 usecs.

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>