ogc: Fix timer precision

[Mefiresu]

SDL_GetPerformanceCounter is supposed to return the value of a high precision counter, but SDL_GetTicks64 returns a truncated value in milliseconds.
Correctly return gettime() as a high precision counter instead, and update SDL_GetPerformanceFrequency accordingly.

[Mefiresu]

For context: I am currently porting Sonic Robo Blast 2 on the Wii, and this game uses a mix of SDL_GetPerformanceFrequency and SDL_GetPerformanceCounter to display performance stats.
The same code worked fine on Wii U (native, not vWii), but didn't on the Wii.

Before timer fix:

After timer fix:

These two functions are often used for deltatime computations in general, so having millisecond precision timers make the frametimes all messy.

[Mefiresu]

@mardy Since the original timer code is yours, could you take a quick look at it?

[mardy]

Thanks for pinging me, I hadn't seen the issue before!

It looks absolutely correct :-)