spmi: pmic-arb: Don't byte swap when reading/writing FIFO

We don't want to swap bytes that we're reading and writing to the
FIFOs when we're running on a big-endian CPU. Doing so causes
problems like where the qcom-spmi-iadc driver can't detect the
type of device because the bytes are all mixed up. Use the raw IO
accessors for these API instead, and collapse pmic_arb_base_read()
into the byte reading API so that we aren't tempted to read non-FIFO
data like commands with that function.

Cc: Andy Gross <agross@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>