clocksource: Increase dependencies of timer-stm32 to limit build wreckage

This driver leaks out into arch/parisc builds that don't have
CONFIG_GENERIC_CLOCKEVENTS, leading to the following (truncated)
wreckage:

  CC      drivers/clocksource/timer-stm32.o
drivers/clocksource/timer-stm32.c:38:28: error: field 'evtdev' has incomplete type
drivers/clocksource/timer-stm32.c:44:19: warning: 'enum clock_event_mode' declared inside parameter list
drivers/clocksource/timer-stm32.c:44:19: warning: its scope is only this definition or declaration, which is probably not what you want
drivers/clocksource/timer-stm32.c:43:62: error: parameter 1 ('mode') has incomplete type
drivers/clocksource/timer-stm32.c:43:13: error: function declaration isn't a prototype
drivers/clocksource/timer-stm32.c: In function 'stm32_clock_event_set_mode':
drivers/clocksource/timer-stm32.c:47:3: error: type defaults to 'int' in declaration of '__mptr'
drivers/clocksource/timer-stm32.c:47:3: warning: initialization from incompatible pointer type
drivers/clocksource/timer-stm32.c:51:7: error: 'CLOCK_EVT_MODE_PERIODIC' undeclared (first use in this function)
drivers/clocksource/timer-stm32.c:51:7: note: each undeclared identifier is reported only once for each function it appears in
drivers/clocksource/timer-stm32.c:56:7: error: 'CLOCK_EVT_MODE_ONESHOT' undeclared (first use in this function)

Tighten up the dependencies to limit where it gets built by copying
the style of the Kconfig line for CLKSRC_EFM32 a few lines above.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: http://lkml.kernel.org/r/1434841352-24300-1-git-send-email-paul.gortmaker@windriver.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>