Using CONFIG_IS_ENABLED() doesn't work in SPL. This patch replaces the only
occurrence of CONFIG_IS_ENABLED() in start.S to a regular #if defined().
It also adds "&& !defined(CONFIG_SPL_BUILD)" to that #if statement because
the spin-table code can't currently work in SPL, and the spin-table file
isn't even compiled in SPL.
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>