Removed external functions from SysCalls.h

* Replace `int` with `s32` as return type for syscalls.
* Renamed `SC_Something.*` files with the proper lv2 name
`sys_something.*`.
* Moving away from the lv2, those functions and folders that doesn't
correspond to lv2 functions. E.g. module functions from sys_io,
sysPrxForUser, cellGcmSys.
* Splitted some files (memory -> memory+mmapper) and merged other ones
(event+event_flag ->event, spu+spu_thread -> spu), according to common
sense, PSDevWiki docs, and checking firmware files.
* Removed external functions from `SysCalls.h`.

NOTE: What should we do about: cellGcmCallback? It's not a lv2 syscall
but it appears on the sc_table and it is actually called in games. Is
this some kind of hack?

rpcs3/Emu/SysCalls/Modules/cellSysutil.h

@@ -213,3 +213,6 @@ struct CellHddGameCBResult
 	be_t<u32> invalidMsg_addr;  // char*
 	be_t<u32> reserved_addr;  // void*
 };
+
+// SysCalls
+s32 cellVideoOutConfigure(u32 videoOut, u32 config_addr, u32 option_addr, u32 waitForEvent);