MAINTAINERS: generify the Microchip RISC-V entry name

These drivers work on our other FPGAs, for example the non-SoC PolarFire
connected to an FU-540 via chiplink. Make the entry a wee bit more
generic to match. While at it, remove the / from the heading so that it
matches other, neighbouring RISC-V entries.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221109212219.1598355-3-conor@kernel.org


Signed-off-by: Arnd Bergmann <arnd@arndb.de>