doc: remove unused CONFIG_ options, fix x-ref to existing ones

Config options KERNEL_EVENT_{INTERRUPT, CONTEXT, SLEEP} don't exist
any more, removed.

Move to use :option:`CONFIG_XYZ` vs :option:`XYZ` to generate propert
links and avoid warnings about unexistant targets.

Change-Id: Ibafa155f474a05329a8cac7bff5c55800d9f31a4
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>