libs/utils/env: use custom platform definition for OAK targets
libs/utils/env: use custom platform definition for OAK targets

The target configuration is defined by two main attributes:
- platform := Linux | Android | Host
- board    := (optional) one of the supported boards

Thus, the "platform" attribute is used just to setup the proper communication
channel abstraction with target (e.g. SSH for Linux or ADB for Android).
Instead, the "board" attribute is used to properly initialise other board
specific supports (e.g. the energy monitor can be HWMON for JUNO/TC2 or a DAQ
for another board).

This patch remove the temporary fix to support OAK boards. Since that
patch OAK targets are now just standard "linux" platforms. Thus the
target configuration fragment to address one of such boards is:

{
   "platform" = "linux",
   "board" = "oak",
}
Signed-off-by: Patrick Bellasi <431c86f368affbc3148c4669fbd465131f7e82cb@arm.com>

bjackman/lisa,credp/lisa,bjackman/lisa,mdigiorgio/lisa,arnoldlu/lisa,joelagnel/lisa,JaviMerino/lisa,mdigiorgio/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa,ARM-software/lisa,credp/lisa,credp/lisa,joelagnel/lisa,ARM-software/lisa,arnoldlu/lisa