clocksource/drivers/hyper-v: Move handling of STIMER0 interrupts

STIMER0 interrupts are most naturally modeled as per-cpu IRQs. But
because x86/x64 doesn't have per-cpu IRQs, the core STIMER0 interrupt
handling machinery is done in code under arch/x86 and Linux IRQs are
not used. Adding support for ARM64 means adding equivalent code
using per-cpu IRQs under arch/arm64.

A better model is to treat per-cpu IRQs as the normal path (which it is
for modern architectures), and the x86/x64 path as the exception. Do this
by incorporating standard Linux per-cpu IRQ allocation into the main
SITMER0 driver code, and bypass it in the x86/x64 exception case. For
x86/x64, special case code is retained under arch/x86, but no STIMER0
interrupt handling code is needed under arch/arm64.

No functional change.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1614721102-2241-11-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

include/asm-generic/mshyperv.h

@@ -183,9 +183,4 @@ static inline bool hv_is_hibernation_supported(void) { return false; }
 static inline void hyperv_cleanup(void) {}
 #endif /* CONFIG_HYPERV */
 
-#if IS_ENABLED(CONFIG_HYPERV)
-extern int hv_setup_stimer0_irq(int *irq, int *vector, void (*handler)(void));
-extern void hv_remove_stimer0_irq(int irq);
-#endif
-
 #endif