core/sleep: set timeout for freeze/thaw operation to 1.5 seconds

core/sleep: set timeout for freeze/thaw operation to 1.5 seconds

A FreezeUnit operation can hang due to the presence of kernel threads
(see last 2 commits). Keeping the default configuration will mean the
system will hang for 25 seconds in suspend waiting for the response. 1.5
seconds should be sufficient for most cases.