MIPS: Remove mips_cache_lock() feature As requested in commit e1390801a3c1a2b6d12fa90be368efc19f5b9bfd ([MIPS] Request for the 'mips_cache_lock()' removal), such feature is no longer needed for current MIPS implementation of U-Boot, and no one in the tree uses it for years. Signed-off-by: Shinya Kuribayashi <skuribay@pobox.com>