ARM: pxa: fix building without IWMMXT

ARM: pxa: fix building without IWMMXT

When CONFIG_IWMMXT, the pxa3xx and pxa27x suspend/resume code
emits some xscale specific instructions, which are rejected
by the assembler, because gcc is built with -march=armv5
-mtune=xscale and passes that option to the assembler:

/tmp/cciHumzr.s:553: Error: selected processor does not support ARM mode `mra r2,r3,acc0'
/tmp/cciHumzr.s:605: Error: selected processor does not support ARM mode `mar acc0,r2,r3'
make[3]: *** [arch/arm/mach-pxa/pxa3xx.o] Error 1
/tmp/cci5MUNu.s:326: Error: selected processor does not support ARM mode `mra r2,r3,acc0'
/tmp/cci5MUNu.s:367: Error: selected processor does not support ARM mode `mar acc0,r2,r3'
make[3]: *** [arch/arm/mach-pxa/pxa27x.o] Error 1

Overriding with -Wa,-march=xscale no longer works, so instead
I'm adding an explict ".arch_extension" directive in all four inline
assembly statements, which should work even if they end up in a different
order in the assembly output.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>