ARM: dts: wpcm450: Add nuvoton,shm = <&shm> to FIU node

ARM: dts: wpcm450: Add nuvoton,shm = <&shm> to FIU node

The Flash Interface Unit (FIU) should have a reference to the Shared
Memory controller (SHM) so that flash access from the host (x86 computer
managed by the WPCM450 BMC) can be blocked during flash access by the
FIU driver.

Fixes: 38abcb0d68767 ("ARM: dts: wpcm450: Add FIU SPI controller node")
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20230129112611.1176517-1-j.neuschaefer@gmx.net
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20230201044158.962417-1-joel@jms.id.au
Signed-off-by: Arnd Bergmann <arnd@arndb.de>