ARM: Avoid compiler optimization for readb, writeb and friends.

ARM: Avoid compiler optimization for readb, writeb and friends.

gcc 4.5.1 seems to ignore (at least some) volatile definitions,
avoid that as done in the kernel.

Reading C99 6.7.3 8 and the comment 114) there, I think it is a bug of that
gcc version to ignore the volatile type qualifier used e.g. in __arch_getl().
Anyway, using a definition as in the kernel headers avoids such optimizations when
gcc 4.5.1 is used.

Maybe the headers as used in the current linux-kernel should be used,
but to avoid large changes, I've just added a small change to the current headers.

Signed-off-by: Alexander Holler <[email protected]>
Signed-off-by: Dirk Behme <[email protected]>
Signed-off-by: Wolfgang Denk <[email protected]>
Cc: Alessandro Rubini <[email protected]>
Tested-by: Thomas Weber <[email protected]>
Acked-by: Alexander Holler <[email protected]>
Tested-by: Alexander Holler <[email protected]>