serial/8250: Limit the omap workarounds to omap1

These workarounds do not apply for CONFIG_ARCH_OMAP2PLUS at all,
so let's make it just CONFIG_ARCH_OMAP1.

This is needed to for ARM common zImage changes for
omap2+ to avoid including plat and mach headers.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>