xhci: replace printk(KERN_DEBUG ...)

This patch replaces the calls to printk(KERN_DEBUG ...)
with either calls to xhci_dbg() or calls to pr_debug(),
depending on whether the xhci_hcd structure is available
at callsite, so that the correspoding debugging messages
are not enabled by default when CONFIG_DYNAMIC_DEBUG option
is set but rather can be enabled dynamically taking advantage
of the dynamic debugging feature.

Also, it adds a newline at the end of debugging messages in
case there is not, so that messages don't appear broken
when printed.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>