sconfig: add cpu device type

In order to enumerate CPU devices that are non-x86 (read: no lapic)
provide a generic 'cpu' device.

Change-Id: Ifeafdad8076935c3448784e6958117002509acbf
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/6824
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

util/sconfig/sconfig.l

@@ -39,6 +39,7 @@ pnp		{yylval.number=PNP; return(BUS);}
 i2c		{yylval.number=I2C; return(BUS);}
 lapic		{yylval.number=APIC; return(BUS);}
 cpu_cluster	{yylval.number=CPU_CLUSTER; return(BUS);}
+cpu		{yylval.number=CPU; return(BUS);}
 domain		{yylval.number=DOMAIN; return(BUS);}
 irq		{yylval.number=IRQ; return(RESOURCE);}
 drq		{yylval.number=DRQ; return(RESOURCE);}