Convert CONFIG_SYS_SPD_BUS_NUM to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_SPD_BUS_NUM

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P2020RDB-PC_36BIT_defconfig b/configs/P2020RDB-PC_36BIT_defconfig
index 8804c7b..8b52134 100644
--- a/configs/P2020RDB-PC_36BIT_defconfig
+++ b/configs/P2020RDB-PC_36BIT_defconfig
@@ -51,6 +51,7 @@
 CONFIG_DM=y
 CONFIG_LBA48=y
 CONFIG_DDR_CLK_FREQ=66666666
+CONFIG_SYS_SPD_BUS_NUM=1
 CONFIG_CHIP_SELECTS_PER_CTRL=1
 CONFIG_SYS_BR0_PRELIM_BOOL=y
 CONFIG_SYS_BR0_PRELIM=0xEF001001