xhci: split allocate interrupter into separate alloacte and add parts

The current function that both allocates and adds the interrupter isn't
optimal when using several interrupters. The array of interrupters need
to be protected with a lock while adding or removing interrupters.
If memory is allocated under the default xhci spinlock then GFP_KERNEL
can't be used.

There is no need to allocate the interrupter memory under the lock, so
split this code into separate unlocked allocate part, and a lock
protected add part.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Message-ID: <20230602144009.1225632-6-mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>