ENGR00176177-1 Add irq count mechanism to interactive governor

ENGR00176177-1 Add irq count mechanism to interactive governor

Add irq count to CPUFreq as a freq change condition.
Because some devices' working mode is unable to issue
CPUFreq change because of low CPU loading, but the cpu
freq will impact these devices' performace significantly.

Interactive govervor will sample the cpu loading as well
as the irq count which is registered. If the
loading or the irq count exceed the threshold we set,
governor will issue an CPUFreq change request.

These devices' irq threshold and enable/disable can be modified
via /sys/devices/system/cpu/cpufreq/interactive/irq_scaling

echo 0xAABBBC to change the default setting as below
AA : irq number
BBB: threshold
C  :enable or disable

Currently only enable USDHC3, USDHC4, GPU, SATA and
USB by default, we can add device to the init struct which is
located in arch/arm/mach-mx6/irq.c.

Signed-off-by: Anson Huang <b20788@freescale.com>