rombios: prevent building with PIC/PIE

rombios: prevent building with PIC/PIE

If the default compiler silently defaults to to -fPIC/-fPIE building
rombios fails:

 ld -melf_i386 -s -r 32bitbios.o tcgbios/tcgbiosext.o util.o pmm.o -o 32bitbios_all.o
 There are undefined symbols in the BIOS:
          U _GLOBAL_OFFSET_TABLE_
 make[10]: *** [Makefile:26: 32bitbios_all.o] Error 11

Prevent the failure by enforcing non-PIC/PIE mode.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>