realtek: consolidate bootargs again

realtek: consolidate bootargs again

Bootargs for devices in the realtek target were previously consolidated
in commit af2cfbda2bf5 ("realtek: Consolidate bootargs"), since all
devices currently use the same arguments.

Commit a75b9e3ecb61 ("realtek: Adding RTL930X sub-target") reverted this
without any argumentation, so let's undo that.

Commit 0b8dfe085180 ("realtek: Add RTL931X sub-target") introduced the
old bootargs also for RTL931x, without providing any actual device
support. Until that is done, let's assume vendors will have done what
they did before, and use a baud rate of 115200.

Fixes: a75b9e3ecb61 ("realtek: Adding RTL930X sub-target")
Signed-off-by: Sander Vanheule <sander@svanheule.net>