[linuxsh-dev] Page handling improvements

[NIIBE Y. <gn...@m1...>]

With suggestion by Kaz Kojima, I've implemented page routines, i.e.,
clear_page/copy_page and such, in assembler.  You can see much
performance improvement on SH-4.  I believe SH-3 also gets faster
(not much, if compared SH-4).  Please try it out.
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