mtd: spi-nor: Fix Cadence QSPI RCU Schedule Stall

mtd: spi-nor: Fix Cadence QSPI RCU Schedule Stall

The current Cadence QSPI driver sometimes caused a
"rcu_sched self-detected stall" while writing large files.

Stall Report:
'# mtd_debug write /dev/mtd1 0 48816464 blob.img
[ 1815.454227] rcu: INFO: rcu_sched self-detected stall on CPU
[ 1815.459789] rcu:     0-....: (2099 ticks this GP) idle=8c6/1/0x40000002
 softirq=6492/6492 fqs=935
[ 1815.468442] rcu:      (t=2100 jiffies g=8749 q=247)
	<snip> (abbreviated backtrace)
[ 1815.772086] [<c05a3ea0>] (cqspi_exec_flash_cmd) (cqspi_read_reg)
[ 1815.786203] [<c05a5488>] (cqspi_read_reg) from (read_sr)
[ 1815.803790] [<c05a0330>] (read_sr) from
	(spi_nor_wait_till_ready_with_timeout)
[ 1815.816610] [<c05a182c>] (spi_nor_wait_till_ready_with_timeout) from
	(spi_nor_write+0x104/0x1d0)
[ 1815.836791] [<c05a1a44>] (spi_nor_write) from (part_write+0x50/0x58)
	<snip>
[ 1815.997961] cadence-qspi ff809000.spi: Flash command execution timed out.
[ 1816.004733] error -110 reading SR
file_to_flash: write, size 0x2e8e150, n 0x2e8e150
write(): Connection timed out

This was caused by a tight loop in cqspi_wait_for_bit(). Fix by using
readl_relaxed_poll_timeout() which sleeps 10us while polling a register.

Fit onto 80 character line by truncating the bool clear parameter

Fixes: 140623410536 ("mtd: spi-nor: Add driver for Cadence Quad SPI Flash Controller")
Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>