arm64: Prevent the use of is_kernel_in_hyp_mode() in hypervisor code

Using is_kernel_in_hyp_mode() in hypervisor code is a pretty bad
mistake. This helper only checks for CurrentEL being EL2, which
is always true.

Make the compilation fail if using the helper in hypervisor context
Whilst we're at it, flag the helper as __always_inline, which it
really should be.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20230609162200.2024064-3-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: Marc Zyngier

arch/arm64/include/asm/virt.h

@@ -110,8 +110,10 @@ static inline bool is_hyp_mode_mismatched(void)
 	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
 }
 
-static inline bool is_kernel_in_hyp_mode(void)
+static __always_inline bool is_kernel_in_hyp_mode(void)
 {
+	BUILD_BUG_ON(__is_defined(__KVM_NVHE_HYPERVISOR__) ||
+		     __is_defined(__KVM_VHE_HYPERVISOR__));
 	return read_sysreg(CurrentEL) == CurrentEL_EL2;
 }