usb: dwc3: core: improve reset sequence

usb: dwc3: core: improve reset sequence

According to Synopsys Databook, we shouldn't be
relying on GCTL.CORESOFTRESET bit as that's only for
debugging purposes. Instead, let's use DCTL.CSFTRST
if we're OTG or PERIPHERAL mode.

Host side block will be reset by XHCI driver if
necessary. Note that this reduces amount of time
spent on dwc3_probe() by a long margin.

We're still gonna wait for reset to finish for a
long time (default to 1ms max), but tests show that
the reset polling loop executed at most 19 times
(modprobe dwc3 && modprobe -r dwc3 executed 1000
times in a row).

Note that this patch was submitted to Linux in 2016 [1], however I can
confirm it is needed to support gadget mode in U-Boot on my device.
While I am referencing this patch from Linux I am in fact taking the
full existing dwc3_core_soft_reset() function from Linux as it exists
in v6.19-rc5, so it may differ slightly from the information in the
2016 patch.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/drivers/usb/dwc3?id=f59dcab176293b646e1358144c93c58c3cda2813

Suggested-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Link: https://lore.kernel.org/r/20260115230135.183158-5-macroalpha82@gmail.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>