x86: Set up a shared syscon numbering schema

Each system controller can have a number to identify it. It can then be
accessed using syscon_get_by_driver_data(). Put this in a shared header
file and update the only current user.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/chromebox_panther_defconfig b/configs/chromebox_panther_defconfig
index 17a94f8..e4a3821 100644
--- a/configs/chromebox_panther_defconfig
+++ b/configs/chromebox_panther_defconfig
@@ -16,6 +16,8 @@
 CONFIG_CMD_TPM=y
 CONFIG_CMD_TPM_TEST=y
 CONFIG_OF_CONTROL=y
+CONFIG_REGMAP=y
+CONFIG_SYSCON=y
 CONFIG_CMD_CROS_EC=y
 CONFIG_CROS_EC=y
 CONFIG_CROS_EC_LPC=y