lpc23xx has 2k of battery RAM that is retained in Deep Power Down mode.
To not overwrite that data it must only be initialized on Power On Reset.
However, RSIR looks the same when waking up from Deep Power Down as it does
on the power-on case.
So use 4 bytes of the backup RAM to keep a signature that is only valid if
memory was retained (no power-on Reset).
A small change to the linker script is required so two sections can be
placed into flash.
- arm_reset was completely undocumented, even though technical details buried
deeply in the data sheet of the LPC2387 are involved in the code
- The attribute "naked" is misplaced, it should only be used when no C code
is present. However, the function consists of C code only
- The attribute "noreturn" has to be used in the declaration [1] of a function,
not in the implementation. Otherwise the caller is not informed and code using
the function will not be optimized.
[1]: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
Rationale 1: The common part made only sense for (some) NXP ARM7 MCUs,
but was misleading for MCUs like the LPC1768.
Rationale 2: The common part was only used by one specific MCU
implementation - no need to outsource it.
This PR converts tabs to white spaces.
The statement I used for the conversion:
```find . -name "*.[ch]" -exec zsh -c 'expand -t 4 "$0" > /tmp/e && mv /tmp/e "$0"' {} \;```
Afterwards, I had a quick overview of the converted files to prevent odd indentation.
