Rename CONFIG_SYS_AUTOLAOD to CONFIG_SYS_DISABLE_AUTOLOAD

The "autoload" environment variable is always checked with env_get_yesno
as it can be set to any form of no.  The default behavior of
env_get_yesno is to return -1 on variables that are not set, which acts
as true in general (we test for non-zero return).  To convert
CONFIG_SYS_AUTOLOAD to Kconfig, given that it was almost always used to
set autoload to no, first rename to CONFIG_SYS_DISABLE_AUTOLOAD for
consistency sake.  Then, make it so that if enabled we set autoload=0 in
the default environment.  Migrate all platforms which set
CONFIG_SYS_AUTOLOAD to non-true or that set autoload to false in their
default environment to using CONFIG_SYS_DISABLE_AUTOLOAD

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am335x_guardian_defconfig b/configs/am335x_guardian_defconfig
index 0dc4bb2..34bef30 100644
--- a/configs/am335x_guardian_defconfig
+++ b/configs/am335x_guardian_defconfig
@@ -59,6 +59,7 @@
 CONFIG_CMD_NAND=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_SYS_DISABLE_AUTOLOAD=y
 CONFIG_CMD_BMP=y
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_CMD_MTDPARTS=y