psplash: create psplash tmpfs mount directory in psplash-init

psplash: create psplash tmpfs mount directory in psplash-init

The psplash binary uses TMPDIR as directory to store the FIFO to
communicate with the psplash tools. This directory can be in any
location an init system determines to be suitable, psplash-init
uses /mnt/ for it. Rather than creating the mount directory in
the recipe, just create it in the init script itself. This allows
other init scripts to use a different location without having
an unnecessary .psplash directory in /mnt.

(From OE-Core rev: dd8c7f2466d94fd8326b962e9bcfc4f42a35da38)

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>