ARM: 8382/1: clocksource: make ARM_TIMER_SP804 depend on GENERIC_SCHED_CLOCK

Commit 5261ef2ea836 ("ARM: 8366/1: move Dual-Timer SP804 driver to
drivers/clocksource") moved SP804 to drivers/clocksource resulting in
it being selectable on platforms/architectures without the config
GENERIC_SCHED_CLOCK enabled. Due to that, it results in the following
build failure(e.g. x86_64 allmodconfig)

drivers/built-in.o: In function `__sp804_clocksource_and_sched_clock_init':
(.init.text+0x1a0e7): undefined reference to `sched_clock_register'

This patch fixes the build by making ARM_TIMER_SP804 depend on
GENERIC_SCHED_CLOCK

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>