ARM: shmobile: r8a7740: Add D4 pm domain support

Add support for the D4 power domain.
This domain contains the Coresight-ETM hardware block.

As long as the ARM debug/perf code doesn't use resource management with
runtime PM support, the D4 power domain must be kept powered to avoid a
crash during resume from s2ram (dbg_cpu_pm_notify() calls
reset_ctrl_regs() unconditionally, causing an undefined instruction
oops).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>