ARM: meson: select HAVE_ARM_TWD and ARM_GLOBAL_TIMER

The 32-bit Meson SoCs use multiple Cortex-A9 (Meson8 and Meson8m2) or
Cortex-A5 (Meson8b) CPU cores. These come with the "ARM global timer"
and "Timer-Watchdog" (aka TWD, which provides both a per-cpu local timer
and watchdog).

Selecting ARM_GLOBAL_TIMER and HAVE_ARM_TWD allows us to add the timers
to the SoC.dtsi files.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>