acpi_cpu.c validation of _CST package

[Rui Paulo]

Hi,
The attached patch adds a missing functionality to acpi_cpu.c
regarding to the revalidation of the _CST package when the notify
handler is called.

This is needed, for example, in Apple MacBooks:
 AC plugged in:
% sysctl dev.cpu.{0,1}.cx_supported
dev.cpu.0.cx_supported: C1/1 C2/1
dev.cpu.1.cx_supported: C1/1 C2/1
 AC plugged out:
% sysctl dev.cpu.{0,1}.cx_supported
dev.cpu.0.cx_supported: C1/1 C2/1 C3/57
dev.cpu.1.cx_supported: C1/1 C2/1 C3/57

I'm not sure if this is the best way to do it and I have doubts about
the locking.

Comments?
-- 
Rui Paulo