am335x evm: Add am335x_evm_spiboot target

This target will move the environment into SPI flash and documents
the expected layout.  We correct the SPL define for where U-Boot is
and remove an unused define.

Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/boards.cfg b/boards.cfg
index beefb53..5766f86 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -233,6 +233,7 @@
 integratorcp_cm946es         arm         arm946es    integrator          armltd         -               integratorcp:CM946ES
 ca9x4_ct_vxp                 arm         armv7       vexpress            armltd
 am335x_evm                   arm         armv7       am335x              ti             am33xx      am335x_evm:SERIAL1,CONS_INDEX=1
+am335x_evm_spiboot           arm         armv7       am335x              ti             am33xx      am335x_evm:SERIAL1,CONS_INDEX=1,SPI_BOOT
 am335x_evm_uart1             arm         armv7       am335x              ti             am33xx      am335x_evm:SERIAL2,CONS_INDEX=2
 am335x_evm_uart2             arm         armv7       am335x              ti             am33xx      am335x_evm:SERIAL3,CONS_INDEX=3
 am335x_evm_uart3             arm         armv7       am335x              ti             am33xx      am335x_evm:SERIAL4,CONS_INDEX=4