[Hexagon] Skip byval arguments when checking parameter attributes

[Hexagon] Skip byval arguments when checking parameter attributes

From the point of view of register assignment, byval parameters are
ignored: a byval parameter is not going to be assigned to a register,
and it will not affect the assignments of subsequent parameters.
When matching registers with parameters in the bit tracker, make sure
to skip byval parameters before advancing the registers.

llvm-svn: 278375