Add dynamic switch of ras events support.

Add dynamic switch of ras events support.

Rasdaemon does not support a way to disable some events by config.
If user want to disable specified event(eg:block_rq_complete), he
should recompile rasdaemon, which is not so convenient.

This patch add dynamic switch of ras event support.You can add
events you want to disabled in /etc/sysconfig/rasdaemon.For example,
`DISABLE="ras:mc_event,block:block_rq_complete"`.Then restart
rasdaemon, these two events will be disabled without recompilation.

[mchehab: make is_disabled_event() static]
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>