arm: actions: rename sysmap-s900 to sysmap-owl

Now that memory maps(for both S700 and S900 SoCs) can be managed using
a common file, rename sysmap-s900 to sysmap-owl to reflect the same.

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Amit Singh Tomar <amittomer25@gmail.com>