[aarch64 NCG] Add better support for sub-word primops

During the intial NCG development, GHC did not have support for
anything below Words.  As such the NCG didn't support any of this
either.  AArch64-Darwin however needs support for subword, as
arguments in excess of the first eight (8) passed via registers
are passed on the stack, and there in a packed fashion.  Thus
ghc learned about subword sizes.  This than lead us to gain
subword primops, and these subsequently highlighted deficiencies
in the AArch64 NCG.

This patch rectifies the ones I found through via the test-suite.
I do not claim this to be exhaustive.

Fixes: #19993

Metric Increase:
    T10421
    T13035
    T13719
    T14697
    T1969
    T9203
    T9872a
    T9872b
    T9872c
    T9872d
    T9961
    haddock.Cabal
    haddock.base
    parsing001