ARM: OMAP: hwmod: Use sysc_fields->srst_shift and get rid of hardcoded SYSC_TYPE2_SOFTRESET_MASK

This is useful when we have broken type2 compliant IPs' where
the softreset shift is not the same as SYSC_TYPE2_SOFTRESET_SHIFT
and hence is overridden using sysc_fields->srst_shift.

We have at least one such instance now with onchip keypad on OMAP5
which has a different softreset shift as compared to other type2
IPs'.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Balaji TK  <balajitk@ti.com>
Tested-by: Sourav Poddar <sourav.poddar@ti.com>
Acked-by: Benoît Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>