Add more texture formats to texconv

[Hamcha]

Formats that need to be supported (list will get updated):

• [x] I4 (0x0)
• [x] I8 (0x1)
• [x] IA4 (0x2)
• [x] IA8 (0x3)
• [x] RGB565 (0x4)
• [x] RGB5A3 (0x5)
• [x] RGBA8 (0x6)
• [x] A8 (0x7)
• [ ] CI4 (0x8)
• [ ] CI8 (0x9)
• [ ] CI14 (0xA)
• [ ] CMPR (DXT1) (0xE)