RFR (XS): 8043207: Add const to Address argument for Assembler::swap

[Mikael Vidstedt]

Please review the following fix which changes one of the Assembler::swap 
methods to take a *const* Address argument instead of a non-const. Some 
of the usages of the swap method pass a const argument, and when 
compiling with gcc the const-ness mismatch means the method cannot be 
resolved which in turn means a compilation error. This is for jdk7u 
(only) - the relevant code has been rewritten in jdk8+ to no longer have 
this problem.

Bug: https://bugs.openjdk.java.net/browse/JDK-8043207
Webrev: http://cr.openjdk.java.net/~mikael/webrevs/8043207/webrev.00/webrev/

Thanks,
Mikael