usb: phy: qusb: Make sure to have expected pulse width

In some cases it is observed that request to generate pulse with
DP/DM line is being schedule out due to usage of usleep_range()
which results into bigger pulse width (bigger than 20ms) than
expected (minimum 20us and max 20ms). Bigger pulse width results
into over voltage condition with charger. Hence fix this issue
by using spinlock to complete pulse generation operation atomically.

Change-Id: Iad6e3deb034b3cf30972d762b55643bd47a2ccf9
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>