bt: hci driver over spi: BlueNRG-MS read until IRQ pin goes low
bt: hci driver over spi: BlueNRG-MS read until IRQ pin goes low

According to BlueNRG-MS ref manual, SPI master shoul read  from
controller as long as IRQ pin is high.
Introduce a new loop within spi_rx_thread to do so. Since
it is now possible to enter read loop with nothing to read, set
a max attempts limit to be sure to exit the loop.

Signed-off-by: Erwan Gouriou <de4d967452b83bb0e37525652734e7d9163b6a4c@linaro.org>
Signed-off-by: Christophe Priouzeau <764d1e7ac3bcfb3c2f77ddc550eda7ed9b72ff9f@st.com>

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