drm: zynqmp_dpsub: Always register bridge

In the Linux kernel, the following vulnerability has been resolved:

drm: zynqmp_dpsub: Always register bridge

We must always register the DRM bridge, since zynqmp_dp_hpd_work_func
calls drm_bridge_hpd_notify, which in turn expects hpd_mutex to be
initialized. We do this before zynqmp_dpsub_drm_init since that calls
drm_bridge_attach. This fixes the following lockdep warning:

[ 19.217084] ------------[ cut here ]------------
[ 19.227530] DEBUG_LOCKS_WARN_ON(lock->magic != lock)
[ 19.227768] WARNING: CPU: 0 PID: 140 at kernel/locking/mutex.c:582 __mutex_lock+0x4bc/0x550
[ 19.241696] Modules linked in:
[ 19.244937] CPU: 0 PID: 140 Comm: kworker/0:4 Not tainted 6.6.20+ #96
[ 19.252046] Hardware name: xlnx,zynqmp (DT)
[ 19.256421] Workqueue: events zynqmp_dp_hpd_work_func
[ 19.261795] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 19.269104] pc : __mutex_lock+0x4bc/0x550
[ 19.273364] lr : __mutex_lock+0x4bc/0x550
[ 19.277592] sp : ffffffc085c5bbe0
[ 19.281066] x29: ffffffc085c5bbe0 x28: 0000000000000000 x27: ffffff88009417f8
[ 19.288624] x26: ffffff8800941788 x25: ffffff8800020008 x24: ffffffc082aa3000
[ 19.296227] x23: ffffffc080d90e3c x22: 0000000000000002 x21: 0000000000000000
[ 19.303744] x20: 0000000000000000 x19: ffffff88002f5210 x18: 0000000000000000
[ 19.311295] x17: 6c707369642e3030 x16: 3030613464662072 x15: 0720072007200720
[ 19.318922] x14: 0000000000000000 x13: 284e4f5f4e524157 x12: 0000000000000001
[ 19.326442] x11: 0001ffc085c5b940 x10: 0001ff88003f388b x9 : 0001ff88003f3888
[ 19.334003] x8 : 0001ff88003f3888 x7 : 0000000000000000 x6 : 0000000000000000
[ 19.341537] x5 : 0000000000000000 x4 : 0000000000001668 x3 : 0000000000000000
[ 19.349054] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffffff88003f3880
[ 19.356581] Call trace:
[ 19.359160] __mutex_lock+0x4bc/0x550
[ 19.363032] mutex_lock_nested+0x24/0x30
[ 19.367187] drm_bridge_hpd_notify+0x2c/0x6c
[ 19.371698] zynqmp_dp_hpd_work_func+0x44/0x54
[ 19.376364] process_one_work+0x3ac/0x988
[ 19.380660] worker_thread+0x398/0x694
[ 19.384736] kthread+0x1bc/0x1c0
[ 19.388241] ret_from_fork+0x10/0x20
[ 19.392031] irq event stamp: 183
[ 19.395450] hardirqs last enabled at (183): [<ffffffc0800b9278>] finish_task_switch.isra.0+0xa8/0x2d4
[ 19.405140] hardirqs last disabled at (182): [<ffffffc081ad3754>] __schedule+0x714/0xd04
[ 19.413612] softirqs last enabled at (114): [<ffffffc080133de8>] srcu_invoke_callbacks+0x158/0x23c
[ 19.423128] softirqs last disabled at (110): [<ffffffc080133de8>] srcu_invoke_callbacks+0x158/0x23c
[ 19.432614] ---[ end trace 0000000000000000 ]---

(cherry picked from commit 61ba791c4a7a09a370c45b70a81b8c7d4cf6b2ae)