regmap: Provide user selectable option to enable regmap

Since apparently enabling all the KUnit tests shouldn't enable any new
subsystems it is hard to enable the regmap KUnit tests in normal KUnit
testing scenarios that don't enable any drivers.  Add a Kconfig option
to help with this and include it in the KUnit all tests config.

Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230712-regmap-kunit-enable-v1-1-13e296bd0204@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/Kconfig

@@ -4,7 +4,7 @@
 # subsystems should select the appropriate symbols.
 
 config REGMAP
-	bool "Register Map support" if KUNIT_ALL_TESTS
+	bool
 	default y if (REGMAP_I2C || REGMAP_SPI || REGMAP_SPMI || REGMAP_W1 || REGMAP_AC97 || REGMAP_MMIO || REGMAP_IRQ || REGMAP_SOUNDWIRE || REGMAP_SOUNDWIRE_MBQ || REGMAP_SCCB || REGMAP_I3C || REGMAP_SPI_AVMM || REGMAP_MDIO || REGMAP_FSI)
 	select IRQ_DOMAIN if REGMAP_IRQ
 	select MDIO_BUS if REGMAP_MDIO
@@ -23,6 +23,16 @@ config REGMAP_KUNIT
 	default KUNIT_ALL_TESTS
 	select REGMAP_RAM
 
+config REGMAP_BUILD
+	bool "Enable regmap build"
+	depends on KUNIT
+	select REGMAP
+	help
+	  This option exists purely to allow the regmap KUnit tests to
+	  be enabled without having to enable some driver that uses
+	  regmap due to unfortunate issues with how KUnit tests are
+	  normally enabled.
+
 config REGMAP_AC97
 	tristate
 

tools/testing/kunit/configs/all_tests.config

@@ -33,5 +33,7 @@ CONFIG_DAMON_PADDR=y
 CONFIG_DEBUG_FS=y
 CONFIG_DAMON_DBGFS=y
 
+CONFIG_REGMAP_BUILD=y
+
 CONFIG_SECURITY=y
 CONFIG_SECURITY_APPARMOR=y