da850: add support to wake up DSP during board init

add support for DSP wake-up by default on DA850/OMAP-L138
during board initialization. Enable hwconfig environment and added
extra env setting through CONFIG_EXTRA_ENV_SETTINGS.
To prevent DSP from being woken up,set the environment variable as,
set hwconfig "dsp:wake=no"

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Nagabhushana Netagunte <nagabhushana.netagunte@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>