Adding this attribute allows to avoid warnings issued by GCC in cases
when 'scb_reset_system' is used as a last call in a function with
"noreturn" attribute set(usually reset handler of some sorts)
This commit add a structure definition that represents the stack frame
layout as it is upon entering exception handler. This is useful when
one wants to alter the exception return address, or get information
about registers state saved by the CPU.
these register definitions are common to all cortex mcus. some of the
registers might not be implemented everywhere (especially the floating
point registers), but defining them does no harm.
this modification does not result in any changes in the example
binaries.
