arm64: use readq() instead of readl() to read 64bit entry_point

Here the entrypoint, declared as a 64 bit integer, is read from
a pointer to 64bit integer but the read is done via readl_relaxed()
which is for 32bit quantities.

All the high bits will thus be lost which change the meaning
of the test against zero done later.

Fix this by using readq_relaxed() instead as it should be for
64bit quantities.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/acpi_parking_protocol.c

@@ -125,7 +125,7 @@ static void acpi_parking_protocol_cpu_postboot(void)
 	struct parking_protocol_mailbox __iomem *mailbox = cpu_entry->mailbox;
 	__le64 entry_point;
 
-	entry_point = readl_relaxed(&mailbox->entry_point);
+	entry_point = readq_relaxed(&mailbox->entry_point);
 	/*
 	 * Check if firmware has cleared the entry_point as expected
 	 * by the protocol specification.