drivers: modem: altair: auto select SPI The Altair hardware is connected to SPI and will not work without SPI support The SPI_EXCHANGE is automaticaly enabled (default y) when SPI is selected. Since SPI is mandatory it should be auto selected Signed-off-by: Alin Jerpelea <alin.jerpelea@sony.com> Approved-by: Gregory Nutt <gnutt@nuttx.org>