imx: re-enable ARM arch timer

imx: re-enable ARM arch timer

Config option `ARM_ARCH_TIMER` has been removed during rebasing onto
5.15 kernel in commit 2b395c298247 ("imx: update config for 5.15").

Anyway, as stated in commit 8cdc356f8c30 ("mediatek: mt7623: Re-enable
ARM arch timer") config option `ARM_ARCH_TIMER` cannot be enabled in the
config directly; it is only selected by `HAVE_ARM_ARCH_TIMER`. We need
to enable the latter in our config.

Fixes: 2b395c298247 ("imx: update config for 5.15")
Reported-by: Piotr Dymacz <pepe2k@gmail.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>