am43xx_evm: timer: do not define CONFIG_TIMER for spl

Since OMAP's spl doesn't support DM currently, do not define
CONFIG_TIMER for spl build.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/am43xx_evm.h b/include/configs/am43xx_evm.h
index de7538f..c3867ef 100644
--- a/include/configs/am43xx_evm.h
+++ b/include/configs/am43xx_evm.h
@@ -144,6 +144,7 @@
 #undef CONFIG_DM_MMC
 #undef CONFIG_DM_SPI
 #undef CONFIG_DM_SPI_FLASH
+#undef CONFIG_TIMER
 #endif
 
 #ifndef CONFIG_SPL_BUILD