soc: fsl: dpio: Remove unused inline function qbman_write_eqcr_am_rt_register

There's no callers in-tree anymore since commit
3b2abda7 ("soc: fsl: dpio: Replace QMAN array mode with ring mode enqueue")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Li Yang <leoyang.li@nxp.com>