clocksource/drivers/nps: Remove EZChip NPS clocksource driver

NPS platform has been removed from ARC port and there are no in-tree
users of it now. So RIP !

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201105212210.1891598-2-vgupta@synopsys.com