soc: renesas: rcar-sysc: Remove rcar_sysc_power_{down,up}() helpers

Until commit 7e8a50df ("soc: renesas: rcar-sysc: Drop legacy
handling"), the rcar_sysc_power_{down,up}() helpers were public, as they
were called by the legacy (pre-DT) CPU power management code on R-Car H1
and R-Car Gen2 before.

As they are just one-line wrappers around rcar_sysc_power(), it makes
sense to just remove them.

This also avoids a bool/helper/bool conversion in rcar_sysc_power_cpu(),
where a bool is checked to call one of two helper functions, which
just call rcar_sysc_power() with hardcoded boolean values again.

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