regformats/regdat.sh generate some *-generated.c files when GDBserver
is built. Each .c file has some static variables, which are only used
within function init_registers_XXX, like this,
We want GDBserver create target descriptions dynamically in each
init_registers_XXXX functions, so this patch moves all the related code
into function init_registers_XXXX, so that the following patch can easily
change function init_registers_XXXX to create target description
dynamically, rather than using current pre-generated array.