math: Add acos implementation

Passes the tests that were submitted to the piglit list

Tested on R600 (Pitcairn)

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Jan Vesely <jan.vesely@rutgers.edu>
math: Add asin implementation

asin(x) = atan2(x, sqrt( 1-x^2 ))

alternatively:
asin(x) = PI/2 - acos(x)

Use the atan2 implementation since it produces slightly shorter bitcode and
R600 machine code.

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Jan Vesely <jan.vesely@rutgers.edu>
math: Add tan implementation

Uses the algorithm:
tan(x) = sin(x) / sqrt(1-sin^2(x))

An alternative is:
tan(x) = sin(x) / cos(x)

Which produces more verbose bitcode and longer assembly.

Either way, the generated bitcode seems pretty nasty and a more optimized
but still precise-enough solution is welcome.

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Jan Vesely <jan.vesely@rutgers.edu>