ARM64: ACPI: enable ACPI_SPCR_TABLE

SBBR mentions SPCR as a mandatory ACPI table.  So enable it for ARM64

Earlycon should be set up as early as possible.  ACPI boot tables are
mapped in arch/arm64/kernel/acpi.c:acpi_boot_table_init() that
is called from setup_arch() and that's where we parse SPCR.
So it has to be opted-in per-arch.

When ACPI_SPCR_TABLE is defined initialization of DT earlycon is
deferred until the DT/ACPI decision is done.  Initialize DT earlycon
if ACPI is disabled.

Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/Kconfig

@@ -4,6 +4,7 @@ config ARM64
 	select ACPI_GENERIC_GSI if ACPI
 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
 	select ACPI_MCFG if ACPI
+	select ACPI_SPCR_TABLE if ACPI
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE

arch/arm64/kernel/acpi.c

@@ -24,6 +24,7 @@
 #include <linux/memblock.h>
 #include <linux/of_fdt.h>
 #include <linux/smp.h>
+#include <linux/serial_core.h>
 
 #include <asm/cputype.h>
 #include <asm/cpu_ops.h>
@@ -206,7 +207,7 @@ void __init acpi_boot_table_init(void)
 	if (param_acpi_off ||
 	    (!param_acpi_on && !param_acpi_force &&
 	     of_scan_flat_dt(dt_scan_depth1_nodes, NULL)))
-		return;
+		goto done;
 
 	/*
 	 * ACPI is disabled at this point. Enable it in order to parse
@@ -226,6 +227,14 @@ void __init acpi_boot_table_init(void)
 		if (!param_acpi_force)
 			disable_acpi();
 	}
+
+done:
+	if (acpi_disabled) {
+		if (earlycon_init_is_deferred)
+			early_init_dt_scan_chosen_stdout();
+	} else {
+		parse_spcr(earlycon_init_is_deferred);
+	}
 }
 
 #ifdef CONFIG_ACPI_APEI