spi: microchip: rename driver file and internal identifiers

spi: microchip: rename driver file and internal identifiers

The spi-microchip-core.c driver provides support for the Microchip
PolarFire SoC (MPFS) "hard" SPI controller. It was originally named
"core" with the expectation that it might also cover Microchip's
CoreSPI "soft" IP, but that never materialized.

The CoreSPI IP cannot be supported by this driver because its register
layout differs substantially from the MPFS SPI controller. In practice
most of the code would need to be replaced to handle those differences
so keeping the drivers separate is the simpler approach.

The file and internal symbols are renamed to reflect MPFS support and
to free up "spi-microchip-core.c" for CoreSPI driver.

Fixes: 9ac8d17694b6 ("spi: add support for microchip fpga spi controllers")
Signed-off-by: Prajna Rajendra Kumar <prajna.rajendrakumar@microchip.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251114104545.284765-2-prajna.rajendrakumar@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>