g: sps do not invoke rx_handler unless data was received
g: sps do not invoke rx_handler unless data was received

There is no point in invoking SPS receive handler if there has been no
data transferred while CS was asserted, as would be the case when the
AP generates the wake up pulse.

Also, make sure that the flag indicating that data was seen is cleared
when the interface is reinitialized, as TPM reset could come during an
SPS transaction.

BRANCH=cr50
BUG=b:68012381
TEST=verified that the AP firmware test passes

Change-Id: I82d63d257b67a715d6dbc540c2d7480e5ff718ff
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/754503
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>
Reviewed-by: Mary Ruthven <81380f3403fed74252e92df3ed012a1819ec6296@chromium.org>
Reviewed-by: Andrey Pronin <53bbebe6910b11f7aa2d1daaa466658eb4cba5f2@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec