msm: thermal: Fix a couple of issue for vdd restriction

1.Change curr_level type to int32_t to support negative level for
disabling vdd restriction
2.Fix vdd_rstr_reg_value_show() to print the correct value.
3.Update vdd_restriction_apply_voltage() and
vdd_restriction_apply_frequency() to change the level only when it's
different from cur_level.
4.Update vdd_restriction_apply_all() to set vdd_rstr_en.enabled
based on the enable counts.
5.Fix multiline comment format.

Change-Id: Ibc4e61ec8b5ce68c5e2a02a1e31e8d8c6ad78b54
Signed-off-by: Jennifer Liu <chihning@codeaurora.org>