Remove all unneeded stuff from the linker script. Now the script only
includes what is actually used: it is easier to understand and change
(we'll add some local ELF sections), and it makes a better reference
for possible porting to a different architecture.
This commit also moves the default libraries from the linker script
itself to the LDFLAGS in Makefile, where they really belong.
CONFIG_DETERMINISTIC_BINARY confirms this makes no difference in
the generated binary (nor the ELF FWIW).
Signed-off-by: Alessandro Rubini <email@example.com>