mlxsw: pci: Add shutdown method in PCI driver

On an arm64 platform with the Spectrum ASIC, after loading and executing
a new kernel via kexec, the following trace [1] is observed. This seems
to be caused by the fact that the device is not properly shutdown before
executing the new kernel.

Fix this by implementing a shutdown method which mirrors the remove
method, as recommended by the kexec maintainer [2][3].

[1]
BUG: Bad page state in process devlink pfn:22f73d
page:fffffe00089dcf40 refcount:-1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2ffff00000000000()
raw: 2ffff00000000000 0000000000000000 ffffffff089d0201 0000000000000000
raw: 0000000000000000 0000000000000000 ffffffffffffffff 0000000000000000
page dumped because: nonzero _refcount
Modules linked in:
CPU: 1 PID: 16346 Comm: devlink Tainted: G B 5.8.0-rc6-custom-273020-gac6b365b1bf5 #44
Hardware name: Marvell Armada 7040 TX4810M (DT)
Call trace:
 dump_backtrace+0x0/0x1d0
 show_stack+0x1c/0x28
 dump_stack+0xbc/0x118
 bad_page+0xcc/0xf8
 check_free_page_bad+0x80/0x88
 __free_pages_ok+0x3f8/0x418
 __free_pages+0x38/0x60
 kmem_freepages+0x200/0x2a8
 slab_destroy+0x28/0x68
 slabs_destroy+0x60/0x90
 ___cache_free+0x1b4/0x358
 kfree+0xc0/0x1d0
 skb_free_head+0x2c/0x38
 skb_release_data+0x110/0x1a0
 skb_release_all+0x2c/0x38
 consume_skb+0x38/0x130
 __dev_kfree_skb_any+0x44/0x50
 mlxsw_pci_rdq_fini+0x8c/0xb0
 mlxsw_pci_queue_fini.isra.0+0x28/0x58
 mlxsw_pci_queue_group_fini+0x58/0x88
 mlxsw_pci_aqs_fini+0x2c/0x60
 mlxsw_pci_fini+0x34/0x50
 mlxsw_core_bus_device_unregister+0x104/0x1d0
 mlxsw_devlink_core_bus_device_reload_down+0x2c/0x48
 devlink_reload+0x44/0x158
 devlink_nl_cmd_reload+0x270/0x290
 genl_rcv_msg+0x188/0x2f0
 netlink_rcv_skb+0x5c/0x118
 genl_rcv+0x3c/0x50
 netlink_unicast+0x1bc/0x278
 netlink_sendmsg+0x194/0x390
 __sys_sendto+0xe0/0x158
 __arm64_sys_sendto+0x2c/0x38
 el0_svc_common.constprop.0+0x70/0x168
 do_el0_svc+0x28/0x88
 el0_sync_handler+0x88/0x190
 el0_sync+0x140/0x180

[2]
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1195432.html

[3]
https://patchwork.kernel.org/project/linux-scsi/patch/20170212214920.28866-1-anton@ozlabs.org/#20116693



Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>