soc: microchip: Fix POLARFIRE_SOC_SYS_CTRL input prompt

The symbol's prompt should be a one-line description, instead of just
duplicating the symbol name.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>