clocksource: Improve GENERIC_CLOCKEVENTS dependency

We regularly run into build errors when a clocksource driver selects
CONFIG_TIMER_OF while CONFIG_GENERIC_CLOCKEVENTS is disabled:

In file included from drivers/clocksource/timer-of.c:25:0:
drivers/clocksource/timer-of.h:35:28: error: field 'clkevt' has incomplete type

At the moment, three drivers can show this behavior: ARMV7M_SYSTICK,
CLKSRC_ST_LPC and CLKSRC_NPS. We could add further dependencies as we did
many times, but I have looked a little bit more at what architectures
are left that don't use GENERIC_CLOCKEVENTS, and this shows that there
is a better solution.

On arch/frv and arch/ia64, we never select CONFIG_GENERIC_CLOCKEVENTS
and we also don't use ARCH_USES_GETTIMEOFFSET, which would
block the clocksource Kconfig menu. On m68k, some platforms use
CONFIG_GENERIC_CLOCKEVENTS, some use ARCH_USES_GETTIMEOFFSET, and some
use neither of them. The good news is that there is no configuration that
does not set CONFIG_GENERIC_CLOCKEVENTS but that wants to enable any of
the Kconfig symbols in the menu, so we can simply replace the dependency
with the stricter one. While in theory one could have a clocksource
driver without the clockevent infrastructure, this seems unlikely
to be relevant in the future any more.

We can probably drop some of the other dependencies as well now,
e.g. there should generally be no reason to depend on CONFIG_ARM
unless the driver uses architecture specific assembly.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>