tools: relocate-rela: Read rela start/end directly from ELF

There is no need to pass section information via parameters.
Let's read text base and rela start/end directly from elf.
It will help with reading other information from ELF for others
architecture. Input to relocate-rela is u-boot binary and u-boot ELF.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/ab7ae14a6e058722e8c608089729e98edf20a08d.1655299267.git.michal.simek@amd.com