media: rkvdec: reduce excessive stack usage in assemble_hw_pps()

media: rkvdec: reduce excessive stack usage in assemble_hw_pps()

The rkvdec_pps had a large set of bitfields, all of which
as misaligned. This causes clang-21 and likely other versions to
produce absolutely awful object code and a warning about very
large stack usage, on targets without unaligned access:

drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c:966:12: error: stack frame size (1472) exceeds limit (1280) in 'rkvdec_vp9_start' [-Werror,-Wframe-larger-than]

Part of the problem here is how all the bitfield accesses are
inlined into a function that already has large structures on
the stack.

Mark set_field_order_cnt() as noinline_for_stack, and split out
the following accesses in assemble_hw_pps() into another noinline
function, both of which now using around 800 bytes of stack in the
same configuration.

There is clearly still something wrong with clang here, but
splitting it into multiple functions reduces the risk of stack
overflow.

Fixes: fde24907570d ("media: rkvdec: Add H264 support for the VDPU383 variant")
Link: https://godbolt.org/z/acP1eKeq9
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>