ARM: shmobile: r8a7740: add PMU information to r8a7740.dtsi

Add PMU information to r8a7740.dtsi. With this
included Armadillo800eva DT reference may use the PMU.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>