ext: hal: Remove Altera HAL from the tree and use a module

Use an external Altera HAL repo instead of keeping a copy in ext/hal.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
diff --git a/modules/Kconfig b/modules/Kconfig
index a534efb..d106078 100644
--- a/modules/Kconfig
+++ b/modules/Kconfig
@@ -3,6 +3,7 @@
 
 comment "Optional modules. Make sure they're installed, via the project manifest."
 
+source "modules/Kconfig.altera"
 source "modules/Kconfig.atmel"
 source "modules/Kconfig.canopennode"
 source "modules/Kconfig.civetweb"