arm64: renesas: Fold mach_cpu_init into board_init_f on R-Car S4/V4H/V4M SPL

The mach_cpu_init() function is not invoked in SPL. Instead of
having two functions, fold mach_cpu_init() into board_init_f(),
which is called very early in the boot process and assures that
the CPG and APMU setup will be invoked before DM is brought up.

Fixes: 37997a214ed1 ("arm: renesas: Use stock lowlevel_init function and remove s_init")
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>