build: Use ifeq/else ifeq/else construction in board config

* Instead of nesting ifeq/else/ifeq/else/endif/endif construction, make
  allows the more readable ifeq/else ifeq/else/endif construction. Use it
  instead.

Change-Id: Ifd2635929799db593e04a13827f05c97e95487e4
diff --git a/config/BoardConfigKernel.mk b/config/BoardConfigKernel.mk
index d8d42aa..01d1e61 100644
--- a/config/BoardConfigKernel.mk
+++ b/config/BoardConfigKernel.mk
@@ -68,11 +68,9 @@
 
 ifeq ($(KERNEL_TOOLCHAIN),)
 KERNEL_TOOLCHAIN_PATH := $(KERNEL_TOOLCHAIN_PREFIX)
-else
-ifneq ($(KERNEL_TOOLCHAIN_PREFIX),)
+else ifneq ($(KERNEL_TOOLCHAIN_PREFIX),)
 KERNEL_TOOLCHAIN_PATH := $(KERNEL_TOOLCHAIN)/$(KERNEL_TOOLCHAIN_PREFIX)
 endif
-endif
 
 ifneq ($(USE_CCACHE),)
     # Detect if the system already has ccache installed to use instead of the prebuilt