C6 state with EOI issue fix for some Intel processors

C6 state with EOI issue fix for some Intel processors

There is an errata in some of Intel processors.

AAJ72. EOI Transaction May Not be Sent if Software Enters Core C6
During an Interrupt Service Routine

If core C6 is entered after the start of an interrupt service routine
but before a write to the APIC EOI register, the core may not send an
EOI transaction (if needed) and further interrupts from the same
priority level or lower may be blocked.

This patch fix this issue, by checking if ISR is pending before enter
deep Cx state. If so, it would use power->safe_state instead of deep
Cx state to prevent the above issue happen.

Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>