io: change readX_relaxed() to remove barriers

Now that we hardened readX() API in asm-generic version, readX_relaxed()
API is violating the rules when readX_relaxed() == readX() in the default
implementation.

The relaxed API shouldn't have any barriers in it and it doesn't provide
any ordering with respect to the memory transactions. The only requirement
is for reads to be ordered with respect to each other. This is achieved
by the volatile in the __raw_readX() API.

Open code the relaxed API and remove any barriers in it.

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>