ARM: shmobile: r8a7779: Remove legacy PM Domain remainings

As of commit c99cd90d ("ARM: shmobile: r8a7779: Remove legacy
SoC code"), r8a7779_init_pm_domains() is no longer called.

Remove all related legacy PM Domain code.

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