USB: android: Initialize only serial boot ports

If the usb composition switch is enabling higher
serial interfaces than earlier then adding the second
instance would cause target to crash because the
data structures would not be valid.

Enabling higher serial interface like switching usb
composition from DUN to DUN,NMEA adds the second
instance NMEA but it is not initialized earlier
as the initialization is allowed only once during the
bind config. Limit the serial ports init only for boot
ports and allow only those instances to be added.

Change-Id: I892b3d850dc2e70f98444d7245860dac11ed1030
Signed-off-by: Sujeet Kumar <ksujeet@codeaurora.org>
Signed-off-by: ChandanaKishori Chiluveru <cchilu@codeaurora.org>