[vectorIntrinsics] RFR: Cleanup code for SVML support

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/panama/vector/cleanup.svml/webrev.00/

Considering EnableVectorSupport is turned off by default, SVML entry 
points should be either lazily or unconditionally initialized. 
Considering it's just caching entry point addresses I chose the latter.

Also, some cleanups (new flag to control usage of SVML stubs, renamings, 
etc).

Testing: jdk/incubator/vector tests

Thanks!

Best regards,
Vladimir Ivanov