pseries_platform: Convert the helper script from bash to dash
pseries_platform: Convert the helper script from bash to dash

As some of the scripts (for ex: update flash) can run in dash this
script cannot be invoked. Make the string comparison follow POSIX syntax.

Signed-off-by: Aruna Balakrishnaiah <ab969200bf8a209ae3a660c857a29117d9771707@linux.vnet.ibm.com>

shenki/powerpc-utils,shenki/powerpc-utils,mdroth/powerpc-utils,kamalesh-babulal/powerpc-utils,shenki/powerpc-utils,kamalesh-babulal/powerpc-utils,leitao/powerpc-ibm-utils-debian,kamalesh-babulal/powerpc-utils,leitao/powerpc-ibm-utils-debian,mdroth/powerpc-utils,mdroth/powerpc-utils,leitao/powerpc-ibm-utils-debian