powerpc: mpc85xx: kmp204x: Fix compiling error for usb errata

Commit 92623672 moves USB errata workaround into a C file. This
causes compiling error for kmcoge4 and kmlion1. To enable the
errata workaround, define CONFIG_USB_EHCI_FSL in common header.

Signed-off-by: York Sun <york.sun@nxp.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Ed Swarthout <Ed.Swarthout@nxp.com>
Cc: Sriram Dash <sriram.dash@nxp.com>
Fixes: 92623672 ("fsl: usb: make errata function common for PPC and ARM")