scripts: code_relocate: support section filter

One might want to select the symbols to be relocated inside a file or
a library. To do this, one can use the FILTER argument of
zephyr_code_relocate which must contain a regular expression of the
section names to be selected for relocation.

The test_function_in_sram2 test case in
`tests/application_development/code_relocation` has been updated to
verify that only one function `function_in_sram()` is relocated to ram
and that the function `function_not_relocated()` is not being relocated
when using relocation filter.

Signed-off-by: Sylvain Chouleur <sylvain.chouleur@gmail.com>
Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>