aspeed-g7: trim reserved memory

Remove pcie endpoint, xdma, and espi reserved memory nodes from top level g7 fragment.

Hundreds of MB are reclaimed by removing these nodes - they should only exist for platforms that need them.

Google-Bug-Id: 565469114
Change-Id: I734513d81cc9a94817226ee41aadd6ae3a466d02
Signed-off-by: Sam Agazaryan <samagazaryan@google.com>