src/poky:utils.bbclass: Use objdump instead of readelf to compute SONAME

LLVM has changed the ELF header dump format [1], the code in oe_libinstall
relied upon the format and processed the SONAME inside square brackets
e.g.

0x000000000000000e (SONAME)       Library soname: libreadline.so.8

with older readelf from ( llvm <19 or GNU binutils objdump ) we get

0x000000000000000e (SONAME)       Library soname: [libreadline.so.8]

The check in oe_libinstall will now trip over ELF files read by llvm-readelf
from llvm19+

To make it portable which works across GNU binutils and LLVM tools
switch to using objdump -p to dump the ELF file and modify the regexp
accordingly, as an aside, the post processing expression is simplified
too

[1] llvm/llvm-project#96562

(From OE-Core rev: 11ea8dc57f275057e19db564e6c55d2baea980b0)

Signed-off-by: Khem Raj <raj.khemgmail.com>
Signed-off-by: Richard Purdie <richard.purdielinuxfoundation.org>

Author: kraj