Use `grep -E` or plain `grep` instead of `egrep`

`egrep` has been deprecated in GNU grep since 2007,
and since 3.8 it emits obsolescence warnings:
https://git.savannah.gnu.org/cgit/grep.git/commit/?id=a9515624709865d480e3142fd959bccd1c9372d1


Acked-by: Dhruva Gole <d-gole@ti.com>