IPU: Implement hardware-tested threshold behavior

[F0bes]

As per the manual, TH0 and TH1 are 9 bits wide. Simply increasing this mask would break the intro scene to TearRingSaga Series: Berwick Saga

The second part of the PR fixes that, by properly resetting TH0 and TH1 when IPU_CTRL.RST is set

You can test this as well by using this program ipu_th100.zip

PR:

MASTER:

PS2: (Excuse the poor photography, I haven't had time to set my stuff up properly)

Related PCSX2 issue and PR https://github.com/PCSX2/pcsx2/issues/6057 https://github.com/PCSX2/pcsx2/pull/8001

[jpd002]

Very nice! Thanks a lot for bringing this fix!