Message Handling Unit version is v2.1.

When arm_mhuv2 working with the data protocol transfer mode.
We have split one mhu into two channels, and every channel
include four channel windows, the two channels share
one gic spi interrupt.

There is a problem with the sending scenario.

The first channel will take up 0-3 channel windows, and the second
channel take up 4-7 channel windows. When the first channel send the
data, and the receiver will clear all the four channels status.
Although we only enabled the interrupt on the last channel window with
register CH_INT_EN,the register CHCOMB_INT_ST0 will be 0xf, not be 0x8.
Currently we just clear the last channel windows int status with the
data proctol mode.So after that,the CHCOMB_INT_ST0 status will be 0x7,
not be the 0x0.

Then the second channel send the data, the receiver read the
data, clear all the four channel windows status, trigger the sender
interrupt. But currently the CHCOMB_INT_ST0 register will be 0xf7,
get_irq_chan_comb function will always return the first channel.

So this patch clear all channel windows int status to avoid this interrupt
confusion.
Signed-off-by: Xiaowu.ding <xiaowu.ding@jaguarmicro.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>