ARM: dts: aspeed: Remove flash layout from Facebook AST2500 Common dtsi

Remove FMC flash layout from ast2500-facebook-netbmc-common.dtsi because
flash size and layout varies across different Facebook AST2500 OpenBMC
platforms.

Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
Link: https://lore.kernel.org/r/20200824211948.12852-2-rentao.bupt@gmail.com


Signed-off-by: Joel Stanley <joel@jms.id.au>