AHRS: add update_trig

Calculates helper trig values including cos_roll, cos_pitch
AHRS_DCM: call update_trig
AHRS_HIL: call update_trig
AC_WPNav: use trig values from ahrs
AC_Circle: use trig values from ahrs
AC_PosControl: use trig values from ahrs
AC_AttControl: use trig values from ahrs
Copter: control_acro, drift use trig from ahrs
Copter: remote update_trig from main code