drm/i915: Use kernel_write() in shmem object create

drm/i915: Use kernel_write() in shmem object create

Replace the write_begin/write_end loop in
i915_gem_object_create_shmem_from_data() with call to kernel_write().

This function initializes shmem-backed GEM objects. kernel_write()
simplifies the code by removing manual folio handling.

Part of a series refactoring address_space_operations write_begin and
write_end callbacks to use struct kiocb for passing write context and
flags.

Signed-off-by: Taotao Chen <chentaotao@didiglobal.com>
Link: https://lore.kernel.org/20250716093559.217344-2-chentaotao@didiglobal.com
Signed-off-by: Christian Brauner <brauner@kernel.org>