acpi: Move the table-finding functions into the libary

This is useful for other features. Move the function into library code
so it can be used outside just the 'acpi' command.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/lib/acpi/Makefile b/lib/acpi/Makefile
index 12337ab..c1c9675 100644
--- a/lib/acpi/Makefile
+++ b/lib/acpi/Makefile
@@ -1,6 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0+
 #
 
+obj-y += acpi.o
+
 ifdef CONFIG_$(SPL_TPL_)GENERATE_ACPI_TABLE
 
 obj-$(CONFIG_$(SPL_)ACPIGEN) += acpigen.o