drm/i915/gt: Remove unused function 'dword_in_page'

>> drivers/gpu/drm/i915/gt/intel_lrc.c:17:28: error: unused function 'dword_in_page' [-Werror,-Wunused-function]
   static inline unsigned int dword_in_page(void *addr)

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210109163455.28466-1-chris@chris-wilson.co.uk