Add the rest of the core options, from plain Snes9x Libretro

[anyputer]

Snes9x 2005 / 2005 Plus lacks a whole bunch of core options

• [ ] SuperFX Frequency [snes9x_overclock] (10MHz|20MHz|40MHz|60MHz|80MHz|100MHz)
• [x] Reduce Slowdown (Hack, Unsafe) [snes9x_overclock_cycles] (disabled|compatible|max)
• [x] Reduce Flickering (Hack, Unsafe) [snes9x_reduce_sprite_flicker] (disabled|enabled)
• [ ] Show layer 1 [snes9x_layer_1] (enabled|disabled)
• [ ] Show layer 2 [snes9x_layer_2] (enabled|disabled)
• [ ] Show layer 3 [snes9x_layer_3] (enabled|disabled)
• [ ] Show layer 4 [snes9x_layer_4] (enabled|disabled)
• [ ] Show sprite layer [snes9x_layer_5] (enabled|disabled)
• [ ] Enable graphic clip windows [snes9x_gfx_clip] (enabled|disabled)
• [ ] Enable transparency effects [snes9x_gfx_transp] (enabled|disabled)
• [ ] Enable hires mode [snes9x_gfx_hires] (enabled|disabled)
• [ ] Enable sound channel 1 [snes9x_sndchan_1] (enabled|disabled)
• [ ] Enable sound channel 2 [snes9x_sndchan_2] (enabled|disabled)
• [ ] Enable sound channel 3 [snes9x_sndchan_3] (enabled|disabled)
• [ ] Enable sound channel 4 [snes9x_sndchan_4] (enabled|disabled)
• [ ] Enable sound channel 5 [snes9x_sndchan_5] (enabled|disabled)
• [ ] Enable sound channel 6 [snes9x_sndchan_6] (enabled|disabled)
• [ ] Enable sound channel 7 [snes9x_sndchan_7] (enabled|disabled)
• [ ] Enable sound channel 8 [snes9x_sndchan_8] (enabled|disabled)
• [ ] Crop overscan [snes9x_overscan] (auto|enabled|disabled)
• [ ] Allow Up+Down / Left+Right [snes9x_up_down_allowed] (enabled|disabled)
• [ ] Maybe change Video Mode [catsfc_VideoMode] (auto|NTSC|PAL) to Preferred aspect ratio [snes9x_aspect] (auto|ntsc|pal|4:3) for consistency