cache: Make top level Kconfig menu a boolean dependent on RISCV

The next patch will add a new type of cache maintenance driver responsible
for flushing deeper than is necessary for non coherent DMA (current
use case of drivers/cache drivers), as needed when performing operations
such as memory hotplug and security unlocking of persistent memory. The two
types of operation are similar enough to share a drivers/cache directory
and MAINTAINERS but are otherwise currently unrelated.

To avoid confusion have two separate menus. Each has dependencies that are
implemented by making them boolean symbols, here CACHEMAINT_FOR_DMA
which is dependent on RISCV as all driver are currently for platforms of
that architecture. Set new symbol default to y to avoid breaking existing
configs. This has no affect on actual code built, just visibility of the
menu.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Author: jic23

drivers/cache/Kconfig

@@ -1,9 +1,17 @@
 # SPDX-License-Identifier: GPL-2.0
-menu "Cache Drivers"
+
+menuconfig CACHEMAINT_FOR_DMA
+	bool "Cache management for noncoherent DMA"
+	depends on RISCV
+	default y
+	help
+	  These drivers implement support for noncoherent DMA master devices
+	  on platforms that lack the standard CPU interfaces for this.
+
+if CACHEMAINT_FOR_DMA
 
 config AX45MP_L2_CACHE
 	bool "Andes Technology AX45MP L2 Cache controller"
-	depends on RISCV
 	select RISCV_NONSTANDARD_CACHE_OPS
 	help
 	  Support for the L2 cache controller on Andes Technology AX45MP platforms.
@@ -16,12 +24,11 @@ config SIFIVE_CCACHE
 
 config STARFIVE_STARLINK_CACHE
 	bool "StarFive StarLink Cache controller"
-	depends on RISCV
 	depends on ARCH_STARFIVE
 	depends on 64BIT
 	select RISCV_DMA_NONCOHERENT
 	select RISCV_NONSTANDARD_CACHE_OPS
 	help
 	  Support for the StarLink cache controller IP from StarFive.
 
-endmenu
+endif #CACHEMAINT_FOR_DMA