Fix RetroArch BIOS Locations

[V0rt3x667]

In RetroArch the default behaviour is to have a single system directory to store BIOS & support files. Some cores have hard-coded folders that are searched under the default system directory. I don't like this as I find it untidy and prefer to have folders named after the platforms they support.

Although a directory can be specified via the defaultRAConfigfunction, it creates a file called retroarch.cfg under the platform folder in the config directory. The problem with this is that retroarch.cfg is read by all cores supporting that platform. This leads to the file getting overwritten when a new core is installed.

EXAMPLE: I install lr-fba which sets defaultRAConfig to ${biosdir}/fba for the arcade platform. I then install lr-mame which sets defaultRAConfig to ${biosdir} for the arcade platform. Now retroarch.cfg is overwritten and lr-fba will no longer look for files in ${biosdir}/fba for the arcade platform.

NOTE: setRetroArchCoreOption does not support setting the default system directory.

TARGETS

• Create a folder per core for under the platform folder to prevent overwriting retroarch.cfg. Have this file read and updated with no additional loss of functionality.

[V0rt3x667]

I have added the changes to the main branch.