usb: xhci: split core allocation and initialization

usb: xhci: split core allocation and initialization

Separate allocation and initialization in the xHCI core:
* xhci_mem_init() now only handles memory allocation.
* xhci_init() now only handles initialization.

This split allows xhci_init() to be reused when resuming from S4
suspend-to-disk.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://patch.msgid.link/20260402131342.2628648-11-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>