drm/imagination: Use memdup_user() helper

Switching to memdup_user(), which combines kmalloc() and copy_from_user(),
and it can simplfy code.

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Suggested-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240902023300.1214753-1-ruanjinjie@huawei.com


Signed-off-by: Matt Coster <matt.coster@imgtec.com>