acpi: Create a new Kconfig for ACPI

We have several Kconfig options for ACPI, but all relate to specific
functions, such as generating tables and AML code.

Add a new option which controls including basic ACPI library code,
including the lib/acpi directory. This will allow us to add functions
which are available even if table generation is not supported.

Adjust the command to avoid a build error when ACPIGEN is not enabled.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/lib/Makefile b/lib/Makefile
index 10aa7ac..8d8ccc8 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -66,7 +66,7 @@
 
 obj-y += crypto/
 
-obj-$(CONFIG_$(SPL_TPL_)GENERATE_ACPI_TABLE) += acpi/
+obj-$(CONFIG_$(SPL_TPL_)ACPI) += acpi/
 obj-$(CONFIG_$(SPL_)MD5) += md5.o
 obj-$(CONFIG_ECDSA) += ecdsa/
 obj-$(CONFIG_$(SPL_)RSA) += rsa/