msm: vidc: No need to power on venus for memory allocation/free

Video driver is not writing into any of the venus registers in
__smem_free and __smem_alloc functions. In these calls, it is
not interacting with firmware either. When video driver calls
into SMMU APIs SMMU driver enables the required clocks and
power. So, remove __power_on for these functions.

Change-Id: I0aac163b485cd0d6fe45ac21b0de06d89862c3a1
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>