arch: Add explicit linker script for u-boot-elf

Commit f4dc714aaa2d ("arm64: Turn u-boot.bin back into an ELF file after
relocate-rela")
introduce REMAKE_ELF option to recreate u-boot.elf from u-boot ->
u-boot.bin + DT -> u-boot.elf.

The best is to ilustrate it from make V=1 output
cat u-boot-nodtb.bin dts/dt.dtb > u-boot-dtb.bin
cp u-boot-dtb.bin u-boot.bin
aarch64-linux-gnu-objcopy -I binary -B aarch64 -O elf64-littleaarch64 u-boot.bin u-boot-elf.o
aarch64-linux-gnu-ld.bfd u-boot-elf.o -o u-boot.elf --defsym="_start"=0x8000000 -Ttext=0x8000000

Last command has no explicit linker script passed that's why toolchain
internal linker script is used.
In Binutils 2.32 case it contains SIZEOF_HEADERS symbol which has changed
behavior by commit
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=64029e93683a266c38d19789e780f3748bd6a188
which result in situation that program headers has changed from
(xilinx_zynqmp_mini_defconfig)

Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000010000 0x00000000fffc0000 0x00000000fffc0000
0x0000000000018918 0x0000000000018918 RW 0x10000

to

Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x00000000fffb0000 0x00000000fffb0000
0x0000000000028918 0x0000000000028918 RW 0x10000

Xilinx tools like XSDB or Bootgen are using program headers for loading ELF
to the right location and by above binutils change ELF is loaded to
incorrect location.

The patch is explicitly use u-boot-elf.lds (just cat now) for u-boot.elf
recreation which is called when REMAKE_ELF is setup.
By purpose u-boot-elf.lds doesn't contain OUTPUT_FORMAT/OUTPUT_ARCH to be
able to use by all archs.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Tested-By: Álvaro Fernández Rojas <noltari@gmail.com>