staging: gasket: core: switch to relaxed memory-mapped I/O

Use of readl() is deprecated; readl_relaxed() with appropriate memory
barriers is preferred.  Switch to relaxed reads and writes for better
performance as well.  Memory barriers required for I/O vs. normal
memory access on Apex devices have already been explicitly coded in the
page table routines.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>