arm64: kvm: add prototypes for functions called in asm

A lot of kvm specific functions are called only from assembler
and have no extern prototype, but that causes a W=1 warnings:

arch/arm64/kvm/handle_exit.c:365:24: error: no previous prototype for 'nvhe_hyp_panic_handler' [-Werror=missing-prototypes]
arch/arm64/kvm/va_layout.c:188:6: error: no previous prototype for 'kvm_patch_vector_branch' [-Werror=mi
ssing-prototypes]
arch/arm64/kvm/va_layout.c:287:6: error: no previous prototype for 'kvm_get_kimage_voffset' [-Werror=mis
sing-prototypes]
arch/arm64/kvm/va_layout.c:293:6: error: no previous prototype for 'kvm_compute_final_ctr_el0' [-Werror=
missing-prototypes]
arch/arm64/kvm/hyp/vhe/switch.c:259:17: error: no previous prototype for 'hyp_panic' [-Werror=missing-pr
arch/arm64/kvm/hyp/nvhe/switch.c:389:17: error: no previous prototype for 'kvm_unexpected_el2_exception'
arch/arm64/kvm/hyp/nvhe/switch.c:384:28: error: no previous prototype for 'hyp_panic_bad_stack' [-Werror
arch/arm64/kvm/hyp/nvhe/hyp-main.c:383:6: error: no previous prototype for 'handle_trap' [-Werror=missin
arch/arm64/kvm/hyp/nvhe/psci-relay.c:203:28: error: no previous prototype for 'kvm_host_psci_cpu_entry' [-Werror=missing-prototypes]

Declare those in asm/kvm_asm.h, which already has related declarations.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20230516160642.523862-7-arnd@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>