ipmi: bt-bmc: Use a regmap for register access

The registers for the bt-bmc device live under the Aspeed LPC
controller. Devicetree bindings have recently been introduced for the
LPC controller where the "host" portion of the LPC register space is
described as a syscon device. Future devicetrees describing the bt-bmc
device should nest its node under the appropriate "simple-mfd", "syscon"
compatible node.

This change allows the bt-bmc driver to function with both syscon and
non-syscon- based devicetree descriptions by always using a regmap for
register access, either retrieved from the parent syscon device or
instantiated if none exists.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
index 7f81665..90f3edf 100644
--- a/drivers/char/ipmi/Kconfig
+++ b/drivers/char/ipmi/Kconfig
@@ -78,7 +78,8 @@
 endif # IPMI_HANDLER
 
 config ASPEED_BT_IPMI_BMC
-	depends on ARCH_ASPEED
+	depends on ARCH_ASPEED || COMPILE_TEST
+       depends on REGMAP && REGMAP_MMIO && MFD_SYSCON
 	tristate "BT IPMI bmc driver"
 	help
 	  Provides a driver for the BT (Block Transfer) IPMI interface