mtd: ubi: Update ubi-media.h to dual license

Update license template using SPDX. Move the global layout
of UBI headers to dual license helping UBI to be the standard
solution for raw NAND management.

Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Artem Bityutskiy <dedekind1@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Richard Weinberger <richard@nod.at>