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/cmd/Kconfig b/cmd/Kconfig
index 6ce9e55..157a330 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -190,6 +190,20 @@
 
 menu "Info commands"
 
+config CMD_ACPI
+	bool "acpi"
+	default y if ACPIGEN
+	help
+	  List and dump ACPI tables. ACPI (Advanced Configuration and Power
+	  Interface) is used mostly on x86 for providing information to the
+	  Operating System about devices in the system. The tables are set up
+	  by the firmware, typically U-Boot but possibly an earlier firmware
+	  module, if U-Boot is chain-loaded from something else. ACPI tables
+	  can also include code, to perform hardware-specific tasks required
+	  by the Operating Systems. This allows some amount of separation
+	  between the firmware and OS, and is particularly useful when you
+	  want to make hardware changes without the OS needing to be adjusted.
+
 config CMD_BDI
 	bool "bdinfo"
 	default y