usb: dwc3: make HIRD threshold configurable

HIRD threshold should be configurable by different platforms.

From DesignWare databook:
When HIRD_Threshold[4] is set to 1b1 and HIRD value is greater than or
equal to the value in HIRD_Threshold[3:0], dwc3 asserts output signals
utmi_l1_suspend_n to put PHY into Deep Low-Power mode in L1.

When HIRD_Threshold[4] is set to 1b0 or the HIRD value is less than
HIRD_Threshold[3:0], dwc3 asserts output signals utmi_sleep_n on L1.

Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Change-Id: I58c9d09085c4643a0448441873b31f5f51482129
Git-commit: 460d098cb6728134e0e4ba3d58e10bb43032daa5
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[jackp@codeaurora.org: fixed up trivial merge conflicts]
Signed-off-by: Jack Pham <jackp@codeaurora.org>