ARM: shmobile: Always enable ARCH_TIMER on SoCs with A7 and/or A15

R-Mobile APE6, R-Car Gen2, and RZ/G1 SoCs have Cortex-A7 and/or
Cortex-A15 CPU cores, all of which have ARM architectured timers.

Force use of the ARM architectured timer on these SoCs.
This allows to:
  - Remove the calls to shmobile_init_delay() from the corresponding
    machine vectors,
  - Remove a check in timer setup specific to R-Car Gen2,
  - Remove a check in shmobile_init_delay().

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