[USETUP][SETUPLIB]: Improve how the Setup* INF APIs are interfaced in the code. Define prototypes compatibles (including their calling convention) to the ones defined by setupapi (.h/.dll) so that it can be possible to either use an internal implementation of these functions (via the inflib library), as currently done, or using imported setupapi functions, as would be done by the future 1st-stage GUI installer.
[SETUPLIB]: Cleanup the registry.c file and use the infsupp.h header.
Fixes build that was technically broken since r75247.
[SETUPLIB][USETUP]: Split the registry helper code into registry utility functions (create/mount/unmount/verify hives) and registry creation code (the rest: initializing the system hives) and move it in the setup library. This commit won't correctly compile yet due to problems related to the interfacing of the INF functions.