arm64: smp: Mark IPI globals as __ro_after_init

Mark the three IPI-related globals in smp.c as "__ro_after_init" since
they are only ever set in set_smp_ipi_range(), which is marked
"__init". This is a better and more secure marking than the old
"__read_mostly".
Suggested-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20230906090246.v13.7.I625d393afd71e1766ef73d3bfaac0b347a4afd19@changeidSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/smp.c

@@ -84,9 +84,9 @@ enum ipi_msg_type {
 	MAX_IPI
 };
 
-static int ipi_irq_base __read_mostly;
-static int nr_ipi __read_mostly = NR_IPI;
-static struct irq_desc *ipi_desc[MAX_IPI] __read_mostly;
+static int ipi_irq_base __ro_after_init;
+static int nr_ipi __ro_after_init = NR_IPI;
+static struct irq_desc *ipi_desc[MAX_IPI] __ro_after_init;
 
 static void ipi_setup(int cpu);