components/xen: Actually disable rombios

components/xen: Actually disable rombios

Commit 5fe3855 meant to disable rombios, but didn't.  This causes the following
build failure:

gcc   -O2 -fomit-frame-pointer -m32 -march=i686 -fno-strict-aliasing
-std=gnu99 -Wall -Wstrict-prototypes -Wdeclaration-after-statement
-Wno-unused-but-set-variable -Wno-unused-local-typedefs
-D__XEN_TOOLS__ -MMD -MF .rombios.o.d -D_LARGEFILE_SOURCE
-D_LARGEFILE64_SOURCE -mno-tls-direct-seg-refs  -DNDEBUG -Werror
-fno-stack-protector -fno-exceptions -fno-builtin -msoft-float
-I/usr/local/src/xenboil/raisin/xen-dir-remote/tools/firmware/hvmloader/../../../tools/include
-U__XEN_TOOLS__
-D__XEN_INTERFACE_VERSION__=__XEN_LATEST_INTERFACE_VERSION__
-DENABLE_OVMF -DENABLE_ROMBIOS -DENABLE_SEABIOS  -c -o rombios.o rombios.c
rombios.c: In function ‘rombios_load_roms’:
rombios.c:103:39: error: ‘etherboot’ undeclared (first use in this function)
                                       etherboot);

Disable rombios instead.

Reported-by: Holger Schramm <lists@schramm.by>
Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
---
CC: Stefano Stabellini <sstabellini@kernel.org>