Moved the linux spinlock.h stub into esp_hw_support/include/linux.
esp_hw_support's INCLUDE_DIRS already places include/linux before
include, so the correct include files are picked up for the linux
target.
- Drop the FreeRTOS-Kernel-SMP linux spinlock.h duplicate.
- rv_decode_test: use PRIV_REQUIRES esp_hw_support instead of
hardcoding component include paths.
