Scorpion and Krait don't use the spin-table enable-method.
Instead they rely on mmio register accesses to enable power and
clocks to bring CPUs out of reset. Document their enable-methods.

Cc: <devicetree@vger.kernel.org>
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>
[sboyd: Split off into separate patch, renamed methods to
match compatible nodes]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Kumar Gala <galak@codeaurora.org>