arm64: cpufeature.h: add missing #include of kernel.h

cpufeature.h makes use of DECLARE_BITMAP, which in turn relies on the
BITS_TO_LONGS and DIV_ROUND_UP macros.

This patch includes kernel.h in cpufeature.h to prevent all users having
to do the same thing.
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/cpufeature.h

@@ -31,6 +31,8 @@
 
 #ifndef __ASSEMBLY__
 
+#include <linux/kernel.h>
+
 struct arm64_cpu_capabilities {
 	const char *desc;
 	u16 capability;