ARM: shmobile: R-Mobile: Remove legacy PM Domain code

The last user of the legacy R-Mobile PM Domain code was the r8a7740
legacy SoC code, which has been removed.

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