MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer

Gustavo Pimentel seems to have left Synopsys, so his email is bouncing.
And there is no indication from him expressing willingless to continue
contributing to the driver.

Drop him from the MAINTAINERS entry and add a CREDITS entry.

Link: https://lore.kernel.org/r/20240326085130.12487-1-manivannan.sadhasivam@linaro.org


Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[bhelgaas: add CREDITS entry]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>