meson: Refactor the programmer selection

This implements a positive selection choice of which programmers should
be built.

- Each programmer is represented through an entry in the programmer
  dictionary
- The entry contains:
  - A list of systems and CPU families where the programmer can run on
  - A list of required dependencies
  - A list of sources needed to build the programmer
  - A list of compiler flags
  - A flag to determin if the programmer should be build on 'auto'
- If an entry is not given it is set to the default value
- If a programmer gets selected, an 'active' flag is added to the entry
  on runtime
- All programmers with an 'active' flag will be included in the build
- One or more programmers can be selected through '-Dprogrammer=<>'
  - 'auto' enables all programmers which are available, deps are found
    and have the 'default' flag
  - 'all' enables all programmers which are available and deps are found
  - 'group_***' enables all programmers which are available, deps are
    found and the programmer belongs to the selected group
  - '_programmer_name_' forces the programmer to be built or the build
    will fail.

Change-Id: Ib44b26e3748fc71f116184082b4aed0bb208b4c1
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/63724
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
Reviewed-by: Felix Singer <felixsinger@posteo.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

tests/meson.build

@@ -33,6 +33,10 @@ srcs = [
   'chip_wp.c',
 ]
 
+if not programmer.get('dummy').get('active')
+  srcs += programmer.get('dummy').get('srcs')
+endif
+
 mocks = [
   '-Wl,--wrap=strdup',
   '-Wl,--wrap=physunmap',