Change the type of display port from byte to int

Using byte for display port is error prone since ports
are in the range [0, 255] and bytes have the range [-128, 127].
This way we need to downcast from int to byte in order to write a
value to display port and also we need to call Byte.toUnsignedInt
every time we want to consume it.

Test: m services
Bug: 153334857
Change-Id: I4dce87c0a411c5d447f62cc5564eb4b8a8fb75f0