Add a "noreturn" attribute to 'scb_reset_system'

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)
Fix compile time warnings for 'scb_reset_system'

Adding 'noreturn' to the function cases GCC to issue a warning, since
it still adds standard function's prologue/epilogue. Adding 'naked'
attribute fixes that.
Merge pull request #11 from ndreys/staging

Add a "noreturn" attribute to 'scb_reset_system'