arm: make __image_copy_{start, end} compiler-generated

arm: make __image_copy_{start, end} compiler-generated

This change is only done where needed: some linker
scripts may contain __image_copy_{start,end} yet
remain unchanged.

Also, __image_copy_end needs its own section; putting
it in relocation sections changes their flags and makes
relocation break.

Signed-off-by: Albert ARIBAUD <[email protected]>
Tested-by: Lubomir Popov <[email protected]>
Tested-by: Jeroen Hofstee <[email protected]>
Reviewed-by: Benoît Thébaudeau <[email protected]>