KVM: arm64: Fix compilation when CONFIG_ARM64_USE_LSE_ATOMICS=n

__lse_swap_desc() is compiled unconditionally, even if LSE is disabled
using the config option. Align with the spirit of the config option and
fix some build errors due to __LSE_PREAMBLE being undefined with the
application of some ifdeffery.

Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Link: https://msgid.link/[e-mail]
Signed-off-by: Oliver Upton <[e-mail]>

arch/arm64/kvm/at.c

···
 	}
 }
 
+#ifdef CONFIG_ARM64_LSE_ATOMICS
 static int __lse_swap_desc(u64 __user *ptep, u64 old, u64 new)
 {
 	u64 tmp = old;
···
 
 	return ret;
 }
+#else
+static int __lse_swap_desc(u64 __user *ptep, u64 old, u64 new)
+{
+	return -EINVAL;
+}
+#endif
 
 static int __llsc_swap_desc(u64 __user *ptep, u64 old, u64 new)
 {