Artemis Milestone 2g: Configure Endpoint command

Adds the xHCI Configure Endpoint command for the two bulk endpoints
identified by the previous increment, and fixes control-transfer
sequencing to match the spec: xHCI 1.2 section 4.3.5 requires Configure
Endpoint before SET_CONFIGURATION is sent to the device, the reverse of
the order this driver used through 2f (which happened to work against
QEMU's lenient qemu-xhci emulation but wasn't spec-correct).

New XHCI_TRB_TYPE_CONFIGURE_ENDPOINT_CMD, EP Context type constants for
Bulk IN/OUT, and an XHCI_EP_ADDR_TO_DCI() macro (DCI = 2*EndpointNumber
+ Direction) in xhci.h. xhci_cmd_configure_endpoint() builds the Input
Context (Slot + one EP Context per DCI up to the highest bulk endpoint
in use) and submits the command via the existing next_action deferral
mechanism, correlated on completion via a new
XHCI_CONN_AWAIT_CONFIGURE_ENDPOINT connect_state, then chains into the
existing SET_CONFIGURATION path.

Two allocations had to grow beyond what Address Device sized them for:
the Input Context (previously room for one EP Context only) and, less
obviously, the Device Context that DCBAA[slot_id] itself points at --
the controller only touches DCIs named in a command's own Add/Drop
flags, so growing that buffer required copying its existing Slot+EP0
content forward rather than zeroing it, to avoid handing the controller
a blank EP0 out from under an endpoint this command isn't touching.
Bulk Transfer Rings (bulk_in_ring/bulk_out_ring) are allocated and
wired into the new EP Contexts but not yet exercised by an actual
transfer -- CBW/CSW submission is next.

Verified live via QMP hotplug, all three architectures, byte-identical:
bulk endpoint identification -> configure endpoint command submitted ->
configure endpoint succeeded -> the existing set configuration ->
device configured chain, then a clean disconnect/disable-slot teardown
afterward with the larger Device Context installed.

FABRIC-2.md Section X Milestone 2g's endpoint identify+configure
checklist item marked fully done.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R4VMX6VSKCten8nGgaMkq4

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