drm/i915/lobf: Disintegrate alpm_disable from psr_disable

drm/i915/lobf: Disintegrate alpm_disable from psr_disable

Currently clearing of alpm registers is done through psr_disable()
which is always not correct, without psr also alpm can exist. So
dis-integrate alpm_disable() from psr_disable().

v1: Initial version.
v2:
- Remove h/w register read from alpm_disable(). [Jani]

Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://lore.kernel.org/r/20250423092334.2294483-5-animesh.manna@intel.com