volk: Fix the volk_32fc_s32fc_x2_rotator_32fc_generic kernel

abs() is an int function ...

Call the right one depending on the language now.

Note that I explicitely did the selection here rather than add a lv_abs()
function in volk_complex.h because there is no GCC extension for abs() that
would return the right type, so I'd have to stick to the cabs() function
which would force a double cast back and forth.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
blocks: Add QA tests for the rotator rotateN function which uses VOLK

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
blocks/rotator: Make the input data 'const'

The volk kernels are const and there is no reason to clobber the input

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
blocks: Add a new rotator_cc block to perform frequency shifting

It internally uses the rotator.h helper that was already present,
which in turn makes uses of VOLK rotator kernel

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>