cpu-op lib: Change code layout to remove gcc-4.8 warnings

cpu-op lib: Change code layout to remove gcc-4.8 warnings

gcc-4.8 seems to mistakenly think there are missing field initializers
in the cpu-op.c code, e.g.:

cpu-op.c: In function ‘cpu_op_cmpxchg’:
cpu-op.c:94:4: warning: missing initializer for field ‘src’ of ‘struct <anonymous>’ [-Wmissing-field-initializers]
    .u.memcpy_op.src = (unsigned long)n,

Change the code layout so these warnings are not triggered.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>