Previously we did write the SPSR via an MSR instruction without
additional flags. Unfortunately, this tells the CPU to write the
register only partially. This often isn't a problem as the users PSR
reset value normally is conform to our expectations but in some cases
(e.g. PSR endianess bit on WandBoard core #4) the reset value is bad.
Thus, we have to add the CXSF flags (access Control + eXtension + Status
+ Flags) so the CPU overwrites the entire register.
Fixes#2254
60a7fe5586