sc7180: Increase SPI flash frequency to 37.5MHz

It seems that all SC7180 boards we have can well handle 37.5MHz of SPI
flash speed, so bump that up from the current 25MHz so that we don't
leave boot speed on the table. (The next step would be 50MHz which
currently doesn't work on all boards so we're not going there yet.)

BUG=b:117440651

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: Id6e98fcbc89f5f3bfa408c7e8bbc90b4c92ceeea
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40874
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philip Chen <philipchen@google.com>

src/soc/qualcomm/sc7180/bootblock.c

@@ -22,6 +22,6 @@ void bootblock_soc_init(void)
 {
 	sc7180_mmu_init();
 	clock_init();
-	quadspi_init(25 * MHz);
+	quadspi_init(37500 * KHz);
 	qupv3_fw_init();
 }