mtw(4): Fix warm reboot initialization failures for MT7601U

  The mtw(4) driver works correctly on initial boot, but fails to initialize
  the MT7601U WiFi adapter after a warm reboot.

  Users must either physically unplug and replug the USB adapter, or perform a
  full power cycle to restore functionality, if usb power is always powered
  (only a replug works)

  The root cause is that warm reboot does not power-cycle USB devices,
  leaving the MT7601U in a stale state from the previous session.

  The MCU retains its ready flag and the device ignores initialization
  commands, resulting in timeout waiting for MCU to initialize errors.

  At the OS Level, pinging 1.1.1.1 will work, but the speed will be very
  slow. In addition in debug mode, we see thousand of error logs.

  This patch addresses the issue by:

  * Performing USB re-enumeration on attach to reset the device state
  * Detecting when the MCU is already marked ready (stale from previous
    session) and forcing a reset of the MCU before loading firmware
  * Increasing the firmware load timeout from 3s to 10s to accommodate
    slower initialization after reset
  * Increasing MCU ready poll attempts from 100 to 300 with longer delays
    to handle devices that take longer to become ready after reset

  Note: The increase was random, lower value might work.

Test Plan:

  Tested on MacBook Pro (late-2015) and a MacMini with MediaTek MT7601U
  USB adapter across multiple warm reboot cycles.

  With the mac-mini and a another desktop, the issue happens only if
  connected via an always powered usb hub port in the monitor.
  The laptop don't power cycle it power.

Differential Revision:	https://reviews.freebsd.org/D54659
Reviewed by:	adrian

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