Fix Wdfserial power management checkbox "Allow the computer to turn off this device to save power"

[CristianManca]

Problem

For qcwdfser devices, unchecking "Allow the computer to turn off this device to save power" sets IdleInWorkingState
= 0 and disables selective suspend. Re-checking the box does not restore IdleInWorkingState = 1 — selective suspend
stays disabled until a manual registry edit and device re-enumeration.

Root Cause Analysis

1. EnableSelectiveSuspend never sets Enabled = WdfTrue — when called after re-checking the box, WDF sees
   IdleInWorkingState = 0 in the registry and does not re-enable idle, because the driver provides no explicit
   override. This is the direct cause of the bug.
2. DisableSelectiveSuspend uses a mismatched IdleCaps — it hardcodes IdleCannotWakeFromS0, but WDF locked
   IdleUsbSelectiveSuspend on the first successful enable call. The mismatch causes STATUS_INVALID_DEVICE_REQUEST, so
   the disable call silently fails.
3. DisableSelectiveSuspend does not set UserControlOfIdleSettings — without IdleAllowUserControl, WDF may ignore
   user-initiated power management toggles.

Solution

• Set idleSettings.Enabled = WdfTrue explicitly in EnableSelectiveSuspend when SS should be active, forcing WDF to
  restore IdleInWorkingState = 1 regardless of the registry state.
• Track the accepted IdleCaps in a new DEVICE_CONTEXT field (AssignedIdleCaps), stored after every successful
  WdfDeviceAssignS0IdleSettings call.
• Use pDevContext->AssignedIdleCaps in DisableSelectiveSuspend instead of a hardcoded value, ensuring the IdleCaps
  always matches what WDF locked — across all code paths (normal, STATUS_POWER_STATE_INVALID fallback, and LPC).
• Set UserControlOfIdleSettings = IdleAllowUserControl in DisableSelectiveSuspend so user toggles are honored.

[5656hcx]

The idea to make enabling explicit and store the capabilities is good.

My suggestion is to save this value in the end of function, set and save it only once, and use it in both enable and disable function.