powerpc: Use "grep -E" instead of "egrep"

The latest version of grep claims the egrep is now obsolete so the build
now contains warnings that look like:
	egrep: warning: egrep is obsolescent; using grep -E
fix this up by moving the related file to use "grep -E" instead.

  sed -i "s/egrep/grep -E/g" `grep egrep -rwl arch/powerpc`

Here are the steps to install the latest grep:

  wget http://ftp.gnu.org/gnu/grep/grep-3.8.tar.gz
  tar xf grep-3.8.tar.gz
  cd grep-3.8 && ./configure && make
  sudo make install
  export PATH=/usr/local/bin:$PATH
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1668764429-11540-1-git-send-email-yangtiezhu@loongson.cn

arch/powerpc/boot/wrapper

@@ -594,7 +594,7 @@ ps3)
     # reached, then enter the system reset vector of the partially decompressed
     # image.  No warning is issued.
     rm -f "$odir"/{otheros,otheros-too-big}.bld
-    size=$(${CROSS}nm --no-sort --radix=d "$ofile" | egrep ' _end$' | cut -d' ' -f1)
+    size=$(${CROSS}nm --no-sort --radix=d "$ofile" | grep -E ' _end$' | cut -d' ' -f1)
     bld="otheros.bld"
     if [ $size -gt $((0x1000000)) ]; then
         bld="otheros-too-big.bld"