[dv/fpv] Clean up FPV script and add EndpointType to tlul_assert.sv

This commit strives at eliminating some of the explicitly added demotions (from
assert -> assume) in the fpv.tcl file. In particular, tlul_assert module
contains now a parameter EndpointType that can either be set to "Host" or
"Device", depending on what kind of endpoint it is bound to. Internally, some of
the assertions are switched to assumptions based on that parameter. In order to
keep code duplication to a minimum, the asserted/assumed sequences have been
split out as discrete sequence items such that they are only declared once. The
assertion enable/disable functions had to be revised as well, and the
tlul_assert interface has been changed into a module.

Further, two additional ASSUME macros have been added to prim_assert in order to
support immediate assumptions, and the reqParity assertion in the register file
is changed into an assumption everywhere.

All FPV and DV testbenches have been adapted to use the proper EndpointType.
Note that the behavior of the assertions/assumptions will remain the same for
all DV sims, but it changes the way they behave in FPV.