xhci: fix event ring segment table related masks and variables in header

xHC controller can supports up to 1024 interrupters.
To fit these change the max_interrupters varable from u8 to u16.

Add a separate mask for the reserve and preserve bits [5:0] in the erst
base register and use it instead of the ERST_PRT_MASK.
ERSR_PTR_MASK [3:0] is intended for masking bits in the
event ring dequeue pointer register.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20230202150505.618915-2-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>