accel/ivpu: Split IP and buttress headers

Move buttress registers to ivpu_hw_btrs_*_reg.h headers.
This is an intermediate step before HW layer refactor.

Signed-off-by: Wachowski, Karol <karol.wachowski@intel.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240515113006.457472-2-jacek.lawrynowicz@linux.intel.com