kernel: fix KERNEL_TOOLCHAIN_PATH_gcc and usage

Previously, this would be a full compile prefix
(e.g. prebuilts/gcc/.../bin/aarch64-linux-gnu-). Since we're adding
this to PATH, it only needs to be prebuilts/gcc/.../bin.

Also remove the extra /bin/ added by kernel.mk.

Change-Id: If2490729128c0243c61de646f6c8e19a15c8dc1c

build/tasks/kernel.mk

@@ -188,7 +188,7 @@ ifneq ($(TARGET_KERNEL_MODULES),)
     $(error TARGET_KERNEL_MODULES is no longer supported!)
 endif
 
-PATH_OVERRIDE += PATH=$(KERNEL_TOOLCHAIN_PATH_gcc)/bin:$$PATH
+PATH_OVERRIDE += PATH=$(KERNEL_TOOLCHAIN_PATH_gcc):$$PATH
 
 # System tools are no longer allowed on 10+
 PATH_OVERRIDE += $(TOOLS_PATH_OVERRIDE)

config/BoardConfigKernel.mk

@@ -79,7 +79,7 @@ endif
 
 # We need to add GCC toolchain to the path no matter what
 # for tools like `as`
-KERNEL_TOOLCHAIN_PATH_gcc := $(KERNEL_TOOLCHAIN_$(KERNEL_ARCH))/$(KERNEL_TOOLCHAIN_PREFIX_$(KERNEL_ARCH))
+KERNEL_TOOLCHAIN_PATH_gcc := $(KERNEL_TOOLCHAIN_$(KERNEL_ARCH))
 
 ifneq ($(USE_CCACHE),)
     ifneq ($(CCACHE_EXEC),)