arch: arm: aarch32: Fix syscall inline asm

The inline asm code was not conveying in all cases that registers r1-r3
would get clobbered by the SVC handler code.  In the cases that we can't
list r1-r3 in the clobber list the registers need to show up as outputs
to know that they values are not preserved by the callee.

Fixes #30393

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>