drm/gma500: Rewrite power management code

drm/gma500: Rewrite power management code

Rewrite the power.c code. For some reason this was doing locking +
refcounting + state (suspended or not) bookkeeping all by itself.

But there is no reason for this, this is all taken care of by
the runtime-pm core, through pm_runtime_get()/_put().

Besides this not being necessary the DIY code is also quite weird/
buggy in some places. E.g. power_begin() would manually do a resume
when not resumed already and force_on=true, followed by a
pm_runtime_get(), which will cause a call to gma_power_resume() to
get scheduled which would redo the entire resume again. Which can
all be replaced by a single pm_runtime_get_sync() call.

Note that this is just a cleanup, this does not actually fix
the (disabled through #if 0) runtime-pm support. It does now call
pm_runtime_enable(), but only after doing a pm_runtime_get() at
probe-time, so the device is never runtime suspended.

Doing this permanent get() + enable() instead of not calling
enable() at all is necessary for the pm_runtime_get_if_in_use() call
in gma_power_begin() to work properly.

Note this also removes the gma_power_is_on() call a check like this
without actually holding a reference is always racy, so it is a bad
idea (and therefor has no pm_runtime_foo() equivalent).

The 2 code paths which were using gma_power_is_on() are actually both
guaranteed to only run when the device is powered-on so the 2 checks
can simply be dropped.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220909115646.99920-6-hdegoede@redhat.com