drivers/i2c/tpm: Unconditionally allow I2C TPM ACPI node

DRIVER_I2C_TPM_ACPI is used to enable the "driver" needed for coreboot
to present a TPM node in the devicetree.  It would usually only do so,
if coreboot itself is communicating with the TPM via I2C (I2C_TPM).
However, technically, there is no dependency.

In order to not show the ACPI option in menuconfig if the board is not
using I2C, a dependency was declared in Kconfig.  However, the same can
be achieved without making it an error to manually declare
DRIVER_I2C_TPM_ACPI without I2C_TPM.

For Volteer, we have just such a need, since it has two "sub-variants"
sharing the same overridetree.cb, one having SPI TPM and another having
I2C TPM.  The former will have a disabled ACPI node representing the I2C
TPM, while its Kconfig is such that coreboot itself does not have I2C
TPM support.

In order to export even a disabled ACPI node representing the I2C
connected TPM, coreboot needs DRIVER_I2C_TPM_ACPI.  Hence, that will
have to be enabled in a case where coreboot does not have I2C_TPM (for
one of the two sub-variants, namely volteer2).

BUG=b:173461736
TEST=Tested as part of next CL in chain

Change-Id: I9717f6b68afd90fbc294fbbd2a5b8d0c6ee9ae55
Signed-off-by: Jes Bodi Klinke <jbk@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48222
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/i2c/tpm/Kconfig

@@ -41,8 +41,7 @@ config DRIVER_TPM_I2C_ADDR
 	depends on I2C_TPM
 
 config DRIVER_I2C_TPM_ACPI
-	depends on I2C_TPM
+	bool "Generate I2C TPM ACPI device" if I2C_TPM
-	bool "Generate I2C TPM ACPI device"
 	default y if ARCH_X86 && I2C_TPM
 	default n