psxbios: Better EnterCiritcal implementation

psxbios: Better EnterCiritcal implementation

Nocash documentation says it should return 0 if one or
none of the bits were changed and return 1 of both bits were set.

This fixes Medievil 2, which would freeze upon starting up a game
and this properly fixes Digimon World crashing (with fixed strcat implementation).
It also possibly fix other games.