MAINTAINERS: Update Pistachio platform maintainers

Neither of the current maintainers works for Imagination any more.

Removed both imgtec email addresses and added back mine for
occasional reviews, also changed from Maintained to Odd Fixes to
reflect the time that I will be able to spend on it.

Signed-off-by: James Hartley <james.hartley@sondrel.com>
Patchwork: https://patchwork.linux-mips.org/patch/17475/
Signed-off-by: James Hogan <jhogan@kernel.org>