RFR: 8185062: Set AssumeMP to true and deprecate the flag

[David Holmes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8185062
Webrev: http://cr.openjdk.java.net/~dholmes/8185062/webrev/

Following on from the discussion here:

http://mail.openjdk.java.net/pipermail/hotspot-dev/2017-August/027720.html

and given the new 6 monthly release cadence, it has been decided to 
switch AssumeMP to true and deprecate it in 18.3, with a view to 
obsoleting it and removing all non-MP related code in 18.9.

The SPARC specific setting of AssumeMP is no longer needed, and 
os::is_MP is micro-optimized by checking AssumeMP first.

CSR request: https://bugs.openjdk.java.net/browse/JDK-8188079

Can I please get a reviewer for the CSR request (edit it and add your 
OpenJDK user name to the "Reviewed by" box).

I will push once the CSR request is approved.

Thanks,
David