dm: i2c: allow disabling driver model in SPL

At present if U-Boot proper uses driver model for I2C, then SPL has to
also. While this is desirable, it places a significant barrier to moving
to driver model in some cases. For example, with a space-constrained SPL
it may be necessary to enable CONFIG_SPL_OF_PLATDATA which involves
adjusting some drivers.

This patch introduces a separate Kconfig symbols for enabling DM_I2C and
DM_I2C_GPIO support in SPL.

This will also help to get away from dirty workarounds to
achieve non-DM I2C support for SPL, which is currently used in some
board header files like:

ifdef CONFIG_SPL_BUILD
undef CONFIG_DM_I2C
endif

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index 29aab0f..acd27ac 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -2,9 +2,9 @@
 #
 # (C) Copyright 2000-2007
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
-obj-$(CONFIG_DM_I2C) += i2c-uclass.o
+obj-$(CONFIG_$(SPL_)DM_I2C) += i2c-uclass.o
 ifdef CONFIG_ACPIGEN
-obj-$(CONFIG_DM_I2C) += acpi_i2c.o
+obj-$(CONFIG_$(SPL_)DM_I2C) += acpi_i2c.o
 endif
 obj-$(CONFIG_$(SPL_)DM_I2C_GPIO) += i2c-gpio.o
 obj-$(CONFIG_$(SPL_)I2C_CROS_EC_TUNNEL) += cros_ec_tunnel.o