Convert CONFIG_SKIP_LOWLEVEL_INIT et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SKIP_LOWLEVEL_INIT
   CONFIG_SKIP_LOWLEVEL_INIT_ONLY

In order to do this, we need to introduce SPL and TPL variants of these
options so that we can clearly disable these options only in SPL in some
cases, and both instances in other cases.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/chromebit_mickey_defconfig b/configs/chromebit_mickey_defconfig
index 613da60..f2718c4 100644
--- a/configs/chromebit_mickey_defconfig
+++ b/configs/chromebit_mickey_defconfig
@@ -1,4 +1,5 @@
 CONFIG_ARM=y
+CONFIG_SPL_SKIP_LOWLEVEL_INIT=y
 # CONFIG_SPL_USE_ARCH_MEMCPY is not set
 CONFIG_ARCH_ROCKCHIP=y
 CONFIG_SYS_TEXT_BASE=0x00100000