ARM: mmp: fix timer_read delay

ARM: mmp: fix timer_read delay

[ Upstream commit e348b4014c31041e13ff370669ba3348c4d385e3 ]

timer_read() was using an empty 100-iteration loop to wait for the
TMR_CVWR register to capture the latest timer counter value. The delay
wasn't long enough. This resulted in CPU idle time being extremely
underreported on PXA168 with CONFIG_NO_HZ_IDLE=y.

Switch to the approach used in the vendor kernel, which implements the
capture delay by reading TMR_CVWR a few times instead.

Fixes: 8c975c48b032 ("[ARM] pxa: add base support for Marvell's PXA168 processor line")
Signed-off-by: Doug Brown <doug@schmorgal.com>
Link: https://lore.kernel.org/r/20221204005117.53452-3-doug@schmorgal.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>