arm64: linker: fix: broken tests for fvp_aemv8r_aarch64

What is changed?
Twister tests and sample applications can now run successfully again
for `fvp_aemv8r_aarch64`.
`__kernal_ram_start` is also modified for cortex_m and cortex_a_r
to be consistent with aarch64 linker script and avoid such issue in
the future.

How is it changed?
Modified linker script to make sure that `__kernal_ram_start` to
`__kernal_ram_end` includes both, bss and data, sections as before.

Why do we need this change?
Twister tests and sample applications failed for `fvp_aemv8r_aarch64`
and it was found that commit #87f68b4d
moved the bss section but missed moving the __kernal_ram_start to the
data section which resulted in a crash.

The change is tested with FVP_BaseR_AEMv8R version: 11.27.19.

Signed-off-by: Sudan Landge <sudan.landge@arm.com>