drm/i915/perf: Handle non-power-of-2 reports

Some of the newer OA formats are not powers of 2. For those formats,
adjust the hw_tail accordingly when checking for new reports.

v2: (Ashutosh)
- Switch to OA_TAKEN for diff calculation
- Use OA_BUFFER_SIZE instead of the vma size
- Update comments

Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230323225901.3743681-8-umesh.nerlige.ramappa@intel.com