input: ti_am33x_tsc: Step enable bits made configurable

Current code has hard coded value written to
step enable bits. Now the bits are updated based
on how many steps are needed to be configured got
from platform data.

The user needs to take care not to exceed
the count more than 16. While using ADC and TSC
one should take care to set this parameter correctly.

Sebastian added the common lock and moved the code, that manipulates the
steps, from into the mfd module.

Signed-off-by: Patil, Rachna <rachna@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>