aarch64: Add support for GCS to AArch64 linker

aarch64: Add support for GCS to AArch64 linker

This patch adds support for Guarded Control Stack in AArch64 linker.

This patch implements the following:
1) Defines GNU_PROPERTY_AARCH64_FEATURE_1_GCS bit for GCS in
GNU_PROPERTY_AARCH64_FEATURE_1_AND macro.

2) Adds readelf support to read and print the GNU properties
in AArch64.

Displaying notes found in: .note.gnu.property
[      ]+Owner[        ]+Data size[    ]+Description
  GNU                  0x00000010      NT_GNU_PROPERTY_TYPE_0
      Properties: AArch64 feature: GCS

3) Adds support for the "-z gcs" linker option and document all the values
allowed with this option (-z gcs[=always|never|implicit]) where "-z gcs" is
equivalent to "-z gcs=always" and when this option is not passed in the
command line, it defaults to "implicit".

4) Adds support for the "-z gcs-report" linker option and document all the
values allowed with this option (-z gcs-report[=none|warning|error]) where
"-z gcs-report" is equivalent to "-z gcs-report=none" and when this option
is not passed in the command line, it defaults to "none".

The ABI changes adding GNU_PROPERTY_AARCH64_FEATURE_1_GCS to the
GNU property GNU_PROPERTY_AARCH64_FEATURE_1_AND is merged into main and
can be found in [1].

[1] https://github.com/ARM-software/abi-aa/blob/main/sysvabi64/sysvabi64.rst

Co-authored-by: Matthieu Longo <matthieu.longo@arm.com>
Co-authored-by: Yury Khrustalev <yury.khrustalev@arm.com>