minios: do not export {test,set,clear}_bit etc to applications

minios: do not export {test,set,clear}_bit etc to applications

Fixes ioemu stubdom build:
CC    i386-stubdom/piix4acpi.o
[...]/stubdom/ioemu/hw/piix4acpi.c:272: error: expected ')' before '?' token
[...]/stubdom/ioemu/hw/piix4acpi.c:277: error: conflicting types for 'set_bit'
[...]/stubdom/../extras/mini-os/include/x86/mini-os/os.h:396: error: previous definition of 'set_bit' was here
[...]/stubdom/ioemu/hw/piix4acpi.c:282: error: conflicting types for 'clear_bit'
[...]/stubdom/../extras/mini-os/include/x86/mini-os/os.h:414: error: previous definition of 'clear_bit' was here
[...]/stubdom/ioemu/hw/piix4acpi.c: In function 'gpe_sts_write':

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>