parisc: fixes and cleanups in page cache flushing (2/4)

Implement clear_page_asm and copy_page_asm. These are optimized routines to
clear and copy a page.  I tested prefetch optimizations in clear_page_asm and
copy_page_asm but didn't see any significant performance improvement on rp3440.
I'm not sure if these are routines are significantly faster than memset and/or
memcpy, but they are there for further performance evaluation.

TLB purge operations on PA 1.X SMP machines are now serialized with the help of
the new tlb_lock() and tlb_unlock() macros, since on some PA-RISC machines, TLB
purges need to be serialized in software.  Obviously, lock isn't needed in UP
kernels.  On PA 2.0 machines, there is a local TLB instruction which is much
less disruptive to the memory subsystem.  No lock is needed for local purge.

Loops are also unrolled in flush_instruction_cache_local and
flush_data_cache_local.

The implementation of what used to be copy_user_page (now copy_user_page_asm)
is now fixed. Additionally 64-bit support is now added. Read the preceding
comment which I didn't change.  I left the comment but it is now inaccurate.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>