arch/xtensa: Enable code relocation

Besides adding ARCH_HAS_CODE_DATA_RELOCATION, this patch also adds
support for the "sample_controller" SoC (used by qemu_xtensa) as
demonstration.

As Xtensa lacks a common linker script at the arch level, enabling it
for each platform will be a piecemeal effort. This patch adds it to the
`soc/xtensa/sample_controller` SoC. Basically, default RAMABLE_REGION is
set to be called "RAM", and hooks are inserted so that
gen_relocate_app.py can add the relevant linker bits.

Also, `tests/application_developent/code_relocation` was tweaked to
support the qemu_xtensa platform. Basically, add the relevant linker
script and ensure that relevant memory regions have their program header
(PHDR) associated.

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>