illumos gate

All image data from tem and from imported images (gfx_fb_putimage()) should only operate using BGRA data format. This does allow us to simplify gfx related operations and allows to use the same implementation for UEFI and BIOS VBE.

8-bit indexed colors do have RGB data array already (to be saved in palette registers), all we need is BGRA <-> index translations while transferring data between RAM and framebuffer.
24/32 bit depth is trivial case, we can store this data directly.

15/16 bit depth is a bit more tricky; if we would attempt to store 8-bit component to framebuffer, there would be data loss because of smaller mask size in 15/16 bit mode.
Therefore, we must take account of the mask size of 15/16 bit mode while we are generating BGRA color data. This does address data from terminal emulator.
However, there is secondary source of 32-bit color data - from PNG images. For now, we are addressing PNG case by right sifting color components to match the mask. This technique is not perfect and can cause color distortions, but it is what we have been using so far.

24/32 bit depth is trivial case, we can store this data directly.

Testing done: switch gfx modes with different depths, observe the screen output is correct. No changes in loader behavior, both UEFI and BIOS versions.

Implement bitmap version of UEFI Blt() function.