Allow fully disabling CPU nodes using status = "fail".

This allows a bootloader to change the number of available CPUs (for
example when a common DTS is used for SoC variants with different numbers
of cores) without deleting the nodes altogether, which could require
additional fixups to avoid dangling phandle references.

Unknown status values (everything that is not "okay"/"ok", "disabled" or
"fail"/"fail-...") will continue to be interpreted like "disabled",
meaning that the CPU can be enabled during boot.

References:
- https://www.spinics.net/lists/devicetree-spec/msg01007.html
- https://github.com/devicetree-org/dt-schema/pull/61

Link: https://lore.kernel.org/all/CAL_Jsq+1LsTBdVaODVfmB0eme2jMpNL4VgKk-OM7rQWyyF0Jbw@mail.gmail.com/Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Tested-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Link: https://lore.kernel.org/r/20211122114536.2981-1-matthias.schiffer@ew.tq-group.comSigned-off-by: Rob Herring <robh@kernel.org>