msm: vidc: Unify core_init, load_fw and core_uninit, unload_fw

core_init and load_fw always go hand-in-hand so it is not needed
to expose two different interfaces at msm_vidc_common level. Same
goes for core_uninit and unload_fw.

Change-Id: I8bbc77cfbc6da246d1f0af63c88882b2fd34aff0
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>