Silicon: NXP: Remove direct calls to SwapMmio* APIs

The SwapMmio** APIs are supposed to be called indirectly via
GetMmioOperations** APIs.
Therefore, remove the SwapMmio** APIs from IoAccessLib.h and make
these APIs STATIC to IoAccessLib.c, so that no accidental call can
be made to these.

Signed-off-by: Pankaj Bansal <pankaj.bansal@nxp.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>