iio: documentation: Add out_altvoltage and friends
iio: documentation: Add out_altvoltage and friends

Continuous frequency/clock generating devices, such as DDSs or PLLs
should use out_altvoltage.

Signed-off-by: Michael Hennerich <38f18d03059a1bc88082b55d7ca2d9b1ebfaffe0@analog.com>
Acked-by: Jonathan Cameron <09f65b71b7655725897b2fd41a09a0cefe2e1ace@kernel.org>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs