phy: rcar-gen3-usb2: fix mutex_lock calling in interrupt

phy: rcar-gen3-usb2: fix mutex_lock calling in interrupt

This patch fixes an issue that the extcon_set_cable_state_() is possible
to cause "BUG: scheduling while atomic" because this driver calls
extcon_set_cable_state_() in the interrupt handler and mutex_lock()
is possible to be called by like the following call trace.
So, this patch adds a workqueue function to resolve this issue.

[    9.706504] BUG: scheduling while atomic: systemd-journal/25893/0x00010303
[    9.714569] Modules linked in:
[    9.717629] CPU: 0 PID: 25893 Comm: systemd-journal Not tainted 4.7.0-rc4+ #86
[    9.724844] Hardware name: Renesas Salvator-X board based on r8a7795 (DT)
[    9.731624] Call trace:
[    9.734077] [<ffff0000080889f0>] dump_backtrace+0x0/0x1a8
[    9.739470] [<ffff000008088bac>] show_stack+0x14/0x20
[    9.744520] [<ffff000008348ab4>] dump_stack+0x94/0xb8
[    9.749568] [<ffff0000080da18c>] __schedule_bug+0x44/0x58
[    9.754966] [<ffff0000087c6394>] __schedule+0x4e4/0x598
[    9.760185] [<ffff0000087c6484>] schedule+0x3c/0xa8
[    9.765057] [<ffff0000087c6928>] schedule_preempt_disabled+0x20/0x38
[    9.771408] [<ffff0000080f20dc>] mutex_optimistic_spin+0x18c/0x1d0
[    9.777583] [<ffff0000087c7ef0>] __mutex_lock_slowpath+0x38/0x140
[    9.783669] [<ffff0000087c803c>] mutex_lock+0x44/0x60
[    9.788717] [<ffff00000834ca48>] kobject_uevent_env+0x250/0x500
[    9.794634] [<ffff0000086ae8c0>] extcon_update_state+0x220/0x298
[    9.800634] [<ffff0000086ae9d8>] extcon_set_cable_state_+0x78/0x88
[    9.806812] [<ffff000008376004>] rcar_gen3_device_recognition+0x5c/0xe0
[    9.813420] [<ffff0000083761bc>] rcar_gen3_phy_usb2_irq+0x3c/0x48
[    9.819509] [<ffff0000080fae94>] handle_irq_event_percpu+0x94/0x140
[    9.825769] [<ffff0000080faf88>] handle_irq_event+0x48/0x78
[    9.831334] [<ffff0000080fe620>] handle_fasteoi_irq+0xb8/0x1b0
[    9.837162] [<ffff0000080fa3c4>] generic_handle_irq+0x24/0x38
[    9.842900] [<ffff0000080fa6fc>] __handle_domain_irq+0x5c/0xb8
[    9.848727] [<ffff000008081520>] gic_handle_irq+0x58/0xb0

Reported-by: Simon Horman <horms@verge.net.au>
Fixes: 2b38543c8db1 ("phy: rcar-gen3-usb2: add extcon support")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>