arm64: dts: sm8150: Remove unused 36 MiB memdump region

This reserved memory dump region is intended to be used with the memory
dump v2 driver, but we've disabled that and we don't need this memory
dumping functionality. Remove the unused region and associated driver
node to save 36 MiB of memory.

Signed-off-by: Danny Lin <danny@kdrag0n.dev>