move flash.h to drivers/flash.h and
create a shim for backward-compatibility.
No functional changes to the headers.
A warning in the shim can be controlled with CONFIG_COMPAT_INCLUDES.
Related to #16539
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
Change code from using now deprecated DT_<COMPAT>_<INSTANCE>_<PROP>
defines to using DT_INST_<INSTANCE>_<COMPAT>_<PROP>.
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>