manual: document dependencies on atomic operations

Add atomic operations to the list of generic dependencies.

Since this is an architecture option, there is no comment string to be
added.

Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
[yann.morin.1998@free.fr: use the new arch-option; remove comment string]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>