clk: rockchip: allow grf_type_sys lookup in aux_grf_table

clk: rockchip: allow grf_type_sys lookup in aux_grf_table

Remove the grf_type_sys exclusion from the auxiliary GRF table lookup
in rockchip_clk_register_branches(). Previously, branches with
grf_type_sys always used ctx->grf directly, bypassing the aux_grf_table.

This is a problem on SoCs like RK3588 where ctx->grf points to the
PHP_GRF (set via the CRU's rockchip,grf phandle), but GATE_GRF clock
entries need to access the SYS_GRF instead.

With this change, grf_type_sys branches first check the aux_grf_table,
and fall back to ctx->grf if no entry is found. This is backwards
compatible: on SoCs that do not register grf_type_sys in the
aux_grf_table, the behavior is unchanged.

Reviewed-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Signed-off-by: Daniele Briguglio <hello@superkali.me>
Tested-by: Ricardo Pardini <ricardo@pardini.net>
Link: https://patch.msgid.link/20260419-rk3588-mclk-gate-grf-v4-2-513a42dd1dcc@superkali.me
Signed-off-by: Heiko Stuebner <heiko@sntech.de>