xhci: change 'msix_count' to encompass MSI or MSI-X vectors

xhci: change 'msix_count' to encompass MSI or MSI-X vectors

Instead of variable 'msix_count' containing the number of MSI-X vectors,
now it can contains MSI or MSI-X vector amount. Because both interrupt
methods allow several vectors. Thus, 'msix_count' is renamed to 'nvecs'.

Additionally, instead of storing the maximum possible vector amount,
now it stores the amount of successfully allocated vectors, or negative
integer on allocation failure.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20231201150647.1307406-16-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>