Make lguest compile with CONFIG_BLOCK=n and CONFIG_NET=n

Gabriel C reports lguest doesn't compile with CONFIG_BLOCK=n.  Fix this
by introducing a config var for the block device, which depends on
LGUEST && BLOCK.  Do the same for the net driver, rather then depending
gratuitously on CONFIG_NET.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Gabriel C <nix.or.die@googlemail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/lguest/Kconfig

@@ -1,6 +1,6 @@
 config LGUEST
 	tristate "Linux hypervisor example code"
-	depends on X86 && PARAVIRT && NET && EXPERIMENTAL && !X86_PAE
+	depends on X86 && PARAVIRT && EXPERIMENTAL && !X86_PAE
 	select LGUEST_GUEST
 	select HVC_DRIVER
 	---help---
@@ -18,3 +18,11 @@ config LGUEST_GUEST
 	  The guest needs code built-in, even if the host has lguest
 	  support as a module.  The drivers are tiny, so we build them
 	  in too.
+
+config LGUEST_NET
+	tristate
+	depends on LGUEST_GUEST && NET
+
+config LGUEST_BLOCK
+	tristate
+	depends on LGUEST_GUEST && BLOCK