security/nss: fix build on powerpc64le

Error:
C_Initialize failed: 0x00000030, CKR_DEVICE_ERROR
NSPR error code: -5977: Failure to load dynamic library
Initiailzing softoken failed: 0x00000030, CKR_DEVICE_ERROR
NSPR error code: -5977: Failure to load dynamic library

While here also correct option description after introducing proper VSX option in https://hg.mozilla.org/projects/nss/rev/a66c71152314e591106680e6de618c3c8d044373

(cherry picked from commit 2eaa6b5910ff4c72b61a4fcf4b06c8f6c1d8db93)