Implement RV1106 USB2 PHY signal tuning

Cherry-picked onto the pinned SDK so the ONLY delta versus the pin is this
patch -- the xHCI controller-death investigation needs a controlled build.

The forward-port omitted the vendor driver's rv1106_usb2phy_tuning with the
note "the phy is functional without it". It is functional, but not reliable:
with these registers at reset defaults the HS link is electrically marginal
under sustained traffic, a bulk transfer eventually stalls, and the r8152
Tx-timeout recovery issues an xHCI Stop Endpoint command the controller never
answers. Measured carrier-on to death over four runs: 14s, 519s, 521s, 584s.

Refs flare-edge#160

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MVGTC78dgCGfRANNKjoPea

kernel/rv1106-enablement/usb/rv1106_usb2phy_cfg.c.frag

@@ -1,12 +1,14 @@
  * RV1106 USB2 PHY: single OTG port at 0xff3e0000 (ported from the vendor driver;
  * fields map 1:1 to 6.18 except utmi_iddig -> utmi_id, and the 5.10-only
- * iddig_output/iddig_en/bvalid_grf_sel are dropped). Signal-quality phy_tuning is
- * left off for now (guarded, so NULL is safe): the phy is functional without it.
+ * iddig_output/iddig_en/bvalid_grf_sel are dropped). Signal-quality phy_tuning
+ * was originally left off here; it is now implemented (patches/27-usb-phy-tuning.patch)
+ * because "functional without it" turned out not to mean reliable -- see #160.
  */
 static const struct rockchip_usb2phy_cfg rv1106_phy_cfgs[] = {
 	{
 		.reg = 0xff3e0000,
 		.num_ports	= 1,
+		.phy_tuning	= rv1106_usb2phy_tuning,
 		.clkout_ctl	= { 0x0058, 4, 4, 1, 0 },
 		.port_cfgs	= {
 			[USB2PHY_PORT_OTG] = {