soc: mediatek: PMIC wrap: remove pwrap_is_mt8135() and pwrap_is_mt8173()

With more SoCs being added the list of helper functions like these would
grow. To mitigate this problem we remove the existing helpers and change
the code to test against the pmic type stored inside the pmic specific
datastructure that our context structure points at. There is one usage of
pwrap_is_mt8135() that is ambiguous as the test should not be dependent on
mt8135, but rather on the existence of a bridge. Add a new element to
pmic_wrapper_type to indicate if a bridge is present and use this where
appropriate.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>