The code in common/boot.c collects the different boot entries in
lists of type struct blspec, eventhough many of them may not be
bootloader spec entries but for example boot scripts. This is the first
step of separating the data structures from boot entries and bootloader
spec: As struct blspec is merely a container for collecting boot entries
We simply rename struct blspec to struct bootentries. No functional change.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>