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/include/acpi/acpi_table.h b/include/acpi/acpi_table.h
index 4030d25..7ed0443 100644
--- a/include/acpi/acpi_table.h
+++ b/include/acpi/acpi_table.h
@@ -923,6 +923,14 @@
  */
 ulong write_acpi_tables(ulong start);
 
+/**
+ * acpi_find_table() - Look up an ACPI table
+ *
+ * @sig: Signature of table (4 characters, upper case)
+ * Return: pointer to table header, or NULL if not found
+ */
+struct acpi_table_header *acpi_find_table(const char *sig);
+
 #endif /* !__ACPI__*/
 
 #include <asm/acpi_table.h>