quark_se_ss: power_mgmt: Fix a bug in call to sleep instruction

When sleep instruction is called with interrupts enabled, the
interrupt priority threshold bits need to be set. Only interrupts
with equal or higher priority will wake the sleep. Currently it
is set to 0 unintentionally and only priority 0 interrupt can
wake the sleep.

Jira: ZEP-1349
Change-Id: I927e259345cc37c5ecc4dfdcde996dd16443e61b
Signed-off-by: Ramesh Thomas <ramesh.thomas@intel.com>