Maintainers.txt: Replace Pete with Jeremy as RPi reviewer

First a huge thank you to Pete Batard for all the hard work
landing the RPi code here, and keeping everyone in line.

But, he has lots of commitments, and its time to give him
a breather. As such, I will take over as a platform reviewer.

Cc: Pete Batard <pete@akeo.ie>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Andrei Warkentin <awarkentin@vmware.com>
Cc: Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@arm.com>
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Pete Batard <pete@akeo.ie>
Acked-by: Leif Lindholm <leif@nuviainc.com>