clocksource/drivers/lpc32xx: Support timer-based ARM delay

This commit implements the ARM timer-based delay timer for the
LPC32xx, LPC18xx, LPC43xx family of SoCs.

Also, add a dependency to restrict compiling this driver for
the ARM architecture.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Joachim Eastwood <manabian@gmail.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>