[qemu] Opentitanlib GPIO integration for incoming GPIO signals

[AlexJones0]

Description

A dependency of #27932, related to #27909.

One issue currently blocking the provisioning flows is that the integration of GPIO into OpenTitanLib currently does not handle incoming GPIO signals correctly. This is because:

1. Incoming reads are not correctly buffered and read, causing the host and device GPIO to become out of sync.
2. QEMU has an input forwarding "Y" command that is used but is not documented in its protocol, so support for this needs to be added.

[AlexJones0]

Will be fixed by #28731.