Per the ARMv8 architecture document, modification of the system control
register is a context-changing operation. Context-changing operations are
only guaranteed to be seen after a context synchronization event.
An ISB is a context synchronization event. One has been placed after
each SCTLR modification. Issue was found running full speed on target.
Signed-off-by: Chad Karaginides <quic_chadk@quicinc.com>