BACKPORT: arm64: Create sections.h

BACKPORT: arm64: Create sections.h

Each time new section markers are added, kernel/vmlinux.ld.S is updated,
and new extern char __start_foo[] definitions are scattered through the
tree.

Create asm/include/sections.h to collect these definitions (and include
the existing asm-generic version).

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit ee78fdc71db1ce9a437b9ca17e31063996b71ec1)
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>