MISRA rule 21.15 fix

MISRA rule 21.15 fix

    Rule 21.15: The pointer arguments to the Standard Library functions
    memcpy, memmove and memcmp shall be pointers to qualified or unqualified
    versions of compatible types.

    Basically that means that both pointer arguments must be of the same
    type. However, even if the pointers passed as arguments to the above
    functions are of the same type, Coverity still thinks it's a violation
    if we do pointer arithmetics directly at the function call. Thus the
    pointer arithmetic operations were moved outside of the function
    argument.

    First detected on the following configuration
            make PLAT=fvp LOG_LEVEL=50

    Change-Id: I8b912ec1bfa6f2d60857cb1bd453981fd7001b94
    Signed-off-by: John Tsichritzis <john.tsichritzis@arm.com>