arm64: kernel: re-export _cpu_resume() from sleep.S

Commit b5fe2429 ("arm64: kernel: fix style issues in sleep.S")
changed the linkage of _cpu_resume() to local, even though the symbol
is also referenced from hibernate.c. So revert this change.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/kernel/sleep.S

@@ -107,7 +107,7 @@ ENDPROC(cpu_resume)
 	.ltorg
 	.popsection
 
-_cpu_resume:
+ENTRY(_cpu_resume)
 	mrs	x1, mpidr_el1
 	adr_l	x8, mpidr_hash		// x8 = struct mpidr_hash virt address