dropbear: roll up recipes into mapping lists

dropbear: roll up recipes into mapping lists

this commit removes manual recipes for options and introduces mapping lists:
- DB_OPT_COMMON holds option mappings which are common for all builds;
- DB_OPT_CONFIG holds option mappings which are depend on config settings.

DB_OPT_COMMON is space-separated list of 'words', each of them is in format:
  'header_option|value'

'header_option' is added with value 'value' to 'localoptions.h'.

if 'header_option' is preceded by two exclamation marks ('!!')
then option is not added to 'localoptions.h' but replaced in 'sysoptions.h'.

in short:
   option|value - add option to localoptions.h
 !!option|value - replace option in sysoptions.h

DB_OPT_CONFIG is space-separated list of 'words', each of them is in format:
  'header_option|config_variable|value_enabled|value_disabled'

'header_option' is handled likewise in DB_OPT_COMMON.

if 'config_variable' is enabled (technically: not disabled)
then 'header_option' is set to 'value_enabled' and 'value_disabled' otherwise.

in short:
   option|config|enabled|disabled = add option to localoptions.h
 !!option|config|enabled|disabled = replace option in sysoptions.h

   option := (config) ? enabled : disabled

If you're not sure that option's value doesn't have '|' within - add your recipe
manually right after '$(Build/Configure/dropbear_headers)' and write some words
about your decision.

PS about two exclamation marks:
early idea was to use one exclamation mark to denote such header options
but then i thought single exclamation mark may be overlooked by mistake.

Signed-off-by: Konstantin Demin <rockdrilla@gmail.com>