arm64: sve: Provide sve_cond_update_zcr_vq fallback when !ARM64_SVE

Compilation fails when KVM is selected and ARM64_SVE isn't.

The root cause is that sve_cond_update_zcr_vq is not defined when
ARM64_SVE is not selected. Fix it by adding an empty definition
when CONFIG_ARM64_SVE=n.
Signed-off-by: Xiaofei Tan <tanxiaofei@huawei.com>
[maz: simplified commit message, fleshed out dummy #define]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/1617183879-48748-1-git-send-email-tanxiaofei@huawei.com

arch/arm64/include/asm/fpsimd.h

@@ -168,6 +168,8 @@ static inline int sve_get_current_vl(void)
 static inline void sve_user_disable(void) { BUILD_BUG(); }
 static inline void sve_user_enable(void) { BUILD_BUG(); }
 
+#define sve_cond_update_zcr_vq(val, reg) do { } while (0)
+
 static inline void sve_init_vq_map(void) { }
 static inline void sve_update_vq_map(void) { }
 static inline int sve_verify_vq_map(void) { return 0; }