arch/arm: do not distinguish revisions of ARM1136JF-S

In commit 88cf3bb9
("arch/Config.in.arm: Use armv6k for arm1136jf-s rev1"), Benoît
Thébaudeau added separate options for the revision 0 and revision 1 of
the ARM1136JF-S processor, so that different -march values could be
used (armv6j for revision 0, armv6k for revision 1).

However, this is preventing the removal of the BR2_GCC_TARGET_ARCH
option, which we need to do to give only the CPU type to gcc, and let
it decide the architecture variant that matches. This is because this
story of revision 0 vs. revision 1 is the only case where -mcpu
doesn't fully define the CPU.

Moreover, a quick test with gcc shows that -march=armv6j
-mcpu=arm1136jf-s is accepted, while -march=armv6k -mcpu=arm1136jf-s
makes gcc complain: " warning: switch -mcpu=arm1136jf-s conflicts with
-march=armv6k switch".

In addition, gcc 5 will apparently no longer allow to pass all of
--with-arch, --with-cpu and --with-tune, so we will anyway have to
rely only on one of them.

As a consequence, this commit basically reverts
88cf3bb9 and provides only one option
for ARM1136JF-S. If the two revisions are really different, then they
should be supported in upstream gcc with different -mcpu values.

Note that the removal of the two options should not break existing
full .config, since the hidden option BR2_arm1136jf_s becomes again a
visible option to select the CPU.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>