lib: acpi: Fix linking SPL when ACPIGEN is enabled

lib/acpi/acpigen.o is only compiled into SPL when SPL_ACPIGEN is enabled.
Update several files which reference these functions accordingly.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/root.c b/drivers/core/root.c
index 126b314..d4ae652 100644
--- a/drivers/core/root.c
+++ b/drivers/core/root.c
@@ -426,7 +426,7 @@
 		stats->tag_size;
 }
 
-#ifdef CONFIG_ACPIGEN
+#if CONFIG_IS_ENABLED(ACPIGEN)
 static int root_acpi_get_name(const struct udevice *dev, char *out_name)
 {
 	return acpi_copy_name(out_name, "\\_SB");
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index d5b85f3..a96a8c7 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -3,7 +3,7 @@
 # (C) Copyright 2000-2007
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 obj-$(CONFIG_$(SPL_)DM_I2C) += i2c-uclass.o
-ifdef CONFIG_ACPIGEN
+ifdef CONFIG_$(SPL_)ACPIGEN
 obj-$(CONFIG_$(SPL_)DM_I2C) += acpi_i2c.o
 endif
 obj-$(CONFIG_$(SPL_)DM_I2C_GPIO) += i2c-gpio.o