arm64: kaslr: add kaslr_early_init() declaration

arm64: kaslr: add kaslr_early_init() declaration

kaslr_early_init() is called from assembler code and does not
need a declaration to work, but adding one anyway shuts up
this W=1 warning:

arch/arm64/kernel/pi/kaslr_early.c:88:16: error: no previous prototype for 'kaslr_early_init' [-Werror=missing-prototypes]

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/20230516160642.523862-13-arnd@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>