arch: arm: Kconfig: set default COUNTER_FREQUENCY

Set default COUNTER_FREQUENCY according to config header file
under include/configs/
i.MX6UL/ULL/7D/8QM/8QXP all has system counter frequency run at 8MHz,
so set default value for them.
SUNXI/EXYNOS/ROCKCHIP_RK3128/ROCKCHIP_RK3288/ROCKCHIP_RK322X/ROCKCHIP_RK3036
at 24MHz. ARCH_LX2160A at 25MHz
ARCH_ZYNQMP at 100MHz