librem5-devkit: Enable Rocktech panel

The Kconfig variable name changed upstream

Signed-off-by: Guido Günther <guido.gunther@puri.sm>
3 jobs for devkit-panel-upstream in 53 minutes and 6 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #11980
librem5
build:aarch64:Image

00:32:45

passed #11969
librem5
build:aarch64:deb

00:20:20

failed #11968
librem5
build:aarch64:Image

00:01:58