mesa: Use bitmask/ffs to iterate enabled lights for ff shader keys.
mesa: Use bitmask/ffs to iterate enabled lights for ff shader keys.

Replaces a loop that iterates all lights and test
which of them is enabled by a loop only iterating over
the bits set in the enabled bitmask.

v2: Use _mesa_bit_scan{,64} instead of open coding.
v3: Use u_bit_scan{,64} instead of _mesa_bit_scan{,64}.

Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>
Signed-off-by: Mathias Fröhlich <f51464c0d83b5283880370f10770eaa83440cc6a@web.de>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler