Bug in arch-mmp board selection

[Mark F. Brown]

Hi Eric,

PXA168 and PXA910 are based on PJ1 which is an ARMv5 compatible architecture
MMP2 is a based on PJ4 which configured as ARMv6 currently (there are
ARMv7 versions as well)

Currently all SoCs are selectable under the "PXA168/910/MMP2" menu
option which allows you to then select PXA168, PXA910, and MMP2 boards
for one image. If you build this configuration this error occurs:

  AS      arch/arm/kernel/entry-armv.o
arch/arm/kernel/entry-armv.S: Assembler messages:
arch/arm/kernel/entry-armv.S:212: Error: selected processor does not
support `clrex'
arch/arm/kernel/entry-armv.S:244: Error: selected processor does not
support `clrex'
arch/arm/kernel/entry-armv.S:302: Error: selected processor does not
support `clrex'
arch/arm/kernel/entry-armv.S:338: Error: selected processor does not
support `clrex'
make[1]: *** [arch/arm/kernel/entry-armv.o] Error 1
make: *** [arch/arm/kernel] Error 2

I am aware we can resolve this by adding KConfig rules to prevent this
scenario, but it leads to a deeper question. Why does selecting the
board in turn select the CPU type instead of the user enabling the CPU
type and then providing a set of boards for selection?

e.g.
config MACH_ZYLONITE2
        bool "Marvell's PXA168 Zylonite2 Development Board"
       --> select CPU_PXA168