MIPS: ingenic: Select CPU_SUPPORTS_CPUFREQ && MIPS_EXTERNAL_TIMER

The clock driving the XBurst CPUs in Ingenic SoCs is integer divided
from the main PLL. As such, it is possible to control the frequency of
the CPU, either by changing the divider, or by changing the rate of the
main PLL.

The XBurst CPUs also lack the CP0 timer; the TCU, a separate piece of
hardware in the SoC, provides this functionality.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>