drivers: gpio: add mp2 gpio clock handling

Remove gpio clock management from the GPIO driver when running on the
cortex-m33 on the mp2 and gpio clocks are managed by the cortex-A, being
the resource manager, allowed by the Resource Isolation Framework (RIF).
Also add a specific binding for the mp2 gpio to make clock property
optional.

Signed-off-by: Youssef Zini <youssef.zini@savoirfairelinux.com>