ARM: dts: r8a7743: Add APMU node and second CPU core

Add DT nodes for the Advanced Power Management Unit (APMU) and the
second CPU core.  Use the enable-method to point out that the APMU
should be used for SMP support.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>