iio: qcom-spmi-adc5: Update ADC5 Gen3 conversion request logic

1.Remove mutexes used in TM configure API to avoid deadlock.

2.Update register writes in immediate and TM configure APIs.

3.Correct register and bit to check for end of conversion for immediate
conversion in IRQ handler.

Change-Id: I68d0bc4d6aeef089939d0d9ae9161b6122bf110e
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>