acpi: Add an acpi command

It is useful to dump ACPI tables in U-Boot to see what has been generated.
Add a command to handle this.

To allow the command to find the tables, add a position into the global
data.

Support subcommands to list and dump the tables.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
diff --git a/lib/acpi/acpi_table.c b/lib/acpi/acpi_table.c
index e86df76..1c253af 100644
--- a/lib/acpi/acpi_table.c
+++ b/lib/acpi/acpi_table.c
@@ -240,6 +240,7 @@
 
 	/* Align ACPI tables to 16 byte */
 	acpi_align(ctx);
+	gd->arch.acpi_start = map_to_sysmem(ctx->current);
 
 	/* We need at least an RSDP and an RSDT Table */
 	ctx->rsdp = ctx->current;