Remove unnecessary include of <sys/malloc.h>.

Cleanup i2c bus acquire / release, centralizing all of the logic into
iic_acquire_bus() / iic_release_bus(). "acquire" and "release" hooks
no longer need to be provided by back-end controller drivers (only if
they need special handling, e.g. powering on the i2c controller).
This results in the removal of a bunch of rendundant code from each
back-end controller driver.

Assert that we are not in hard interrupt context in iic_acquire_bus(),
iic_exec(), and iic_release_bus().

branches: 1.2.108;
machine/{bus,cpu,intr}.h -> sys/{bus,cpu,intr}.h

branches: 1.1.2; 1.1.6; 1.1.12; 1.1.18; 1.1.32; 1.1.34; 1.1.38;
Initial import of radeonfb. Works to some degree on at least some hardware.
Most of the testing was done on MIPS hardware -- it probably needs work before
it will be useful with x86 hardware, and it is probably incompatible with
the X11 server.

"ATI Technologies Inc. ("ATI") has not assisted in the creation of, and
does not endorse, this software. ATI will not be responsible or liable
for any actual or alleged damage or loss caused by or in connection with
the use of or reliance on this software."

Enjoy!