sys_prx Improvements

[elad335]

• Implement sys_prx_get_module_list: Used by sys_prx_exitspawn_with_level to get list of modules and call sys_prx_stop_module for each module id, which (I think) is used by exitspawn functions and normal prcosess exit.
• Add missing logic and error codes for sys_prx_start/stop/unload_module.

[sampletext32]

Shouldn't you remove very first sys_prx.todo? Because function is somehow implemented, even not fully, but you add new todos that specify the work. @elad335

[elad335]

The general use of the public "sys_prx_get_module_list" frunction from https://github.com/RPCS3/rpcs3/blob/master/rpcs3/Emu/Cell/Modules/sys_prx_.cpp#L199 is implemented here, but there more uses to the syscall which are not implemented here so the TODO is still needed.
Basically only bit 1 of "flags" arguments handling is implemented here, but the other bit is not.
@sampletext32

[sampletext32]

So, the "todo" should be more precise, not general. So if you cover one bit, todo should cover the other. It would help in future problems investigations. Correct me, if I am wrong.

[elad335]

Ok, done. @sampletext32