ACPI / PMIC: XPower: optimize I2C-bus accesses

The I2C-bus to the XPower AXP288 is shared between the Linux kernel and
the SoCs P-Unit. The P-Unit has a semaphore which the kernel must "lock"
before it may use the bus and while the kernel holds the semaphore the CPU
and GPU power-states must not be changed otherwise the system will freeze.

This is a complex process, which is quite expensive. This is all done by
iosf_mbi_block_punit_i2c_access(). To ensure that no unguarded I2C-bus
accesses happen, iosf_mbi_block_punit_i2c_access() gets called by the
I2C-bus-driver for every I2C transfer. Because this is so expensive it
is allowed to call iosf_mbi_block_punit_i2c_access() in a nested
fashion, so that higher-level code which does multiple I2C-transfers can
call it once for a group of transfers, turning the calls done by the
I2C-bus-driver into no-ops.

Add iosf_mbi_block_punit_i2c_access() calls around groups of register
accesses, so that the P-Unit semaphore only needs to be taken once
for each group of register accesses.

Reviewed-by: Andy Shevchenko <[email protected]>
Signed-off-by: Hans de Goede <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

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