x86, olpc: Fix dependency on POWER_SUPPLY

As reported by Randy Dunlap, CONFIG_POWER_SUPPLY=m caused a
compile error:

  arch/x86/built-in.o: In function `battery_status_changed':
   olpc-xo15-sci.c:(.text+0x3acdd): undefined reference to `power_supply_get_by_name'
   olpc-xo15-sci.c:(.text+0x3ad04): undefined reference to `power_supply_changed'

The SCI drivers, as bool, require POWER_SUPPLY to be builtin.
Use select to make that a hard requirement and avoid this build
failure.
Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/Kconfig

@@ -2089,7 +2089,8 @@ config OLPC_XO1_RTC
 
 config OLPC_XO1_SCI
 	bool "OLPC XO-1 SCI extras"
-	depends on OLPC && OLPC_XO1_PM && POWER_SUPPLY
+	depends on OLPC && OLPC_XO1_PM
+	select POWER_SUPPLY
 	select GPIO_CS5535
 	select MFD_CORE
 	---help---
@@ -2103,7 +2104,8 @@ config OLPC_XO1_SCI
 
 config OLPC_XO15_SCI
 	bool "OLPC XO-1.5 SCI extras"
-	depends on OLPC && ACPI && POWER_SUPPLY
+	depends on OLPC && ACPI
+	select POWER_SUPPLY
 	---help---
 	  Add support for SCI-based features of the OLPC XO-1.5 laptop:
 	   - EC-driven system wakeups