mali_kbase: platform: use exynos_pd API instead of CAL-IF

exynos_pd keeps track of PD ON/OFF requests and stats.
struct exynos_pm_domain should be opaque to clients but is
not enforced right now.

Use exynos_pd API to keep power state consistent and get stats
reporting accurate.

Also remove the extra call to cal_pd_status which is ensured
by power ON/OFF sequence waiting on the status bit.

Bug: 175668627
Signed-off-by: Thierry Strudel <tstrudel@google.com>
Change-Id: Idc0bbe40c78e1aeb038cf08ad124500d65c721b0