Fix framebuffer configuration race

[JoshMcguigan]

Fixes #5, fixes #28

Details

Previously the arm9 tried to use the framebuffer configuration passed in from the previous bootloader stage. However, the arm11 reconfigured the framebuffer to a new location shortly after power up. This led to the arm9 writing to a memory area which no longer displayed anything on the screen. And since the arm9 was no longer initializing the actual framebuffer random data was displayed on screen.

The fix was to introduce another synchronization point between the arm9 and arm11. The arm9 start.S now waits for the arm11 to have reconfigured the framebuffer before entering main.

This still left a minor flicker of unitialized data between the time that the arm11 moved the framebuffer memory location and when the arm9 initialized that memory - so an additional change in this commit is to have the arm11 initialize that memory before updating the framebuffer location.

Testing

Before:

Rather than displaying the output of firm_linux_loader, random data is displayed up until the time that linux takes over each screen.

IMG_6104-1.mov

After:

The frame buffer is properly initialized, output of firm_linux_loader is visible up until the time that linux takes over each screen.

IMG_6106-1.mov

[JoshMcguigan]

tagging @Wolfvak as requested