net: ipa: don't define unneeded GSI register offsets

Each GSI execution environment (EE) is able to access many of the
GSI registers associated with the other EEs.  A block of GSI
registers is contained within a region of memory, and an EE's
register offset can be determined by adding the register's base
offset to the product of the EE ID and a fixed constant.

Despite this possibility, the AP IPA code *never* accesses any GSI
registers other than its own.  So there's no need to define the
macros that compute register offsets for other EEs.

Redefine the AP access macros to compute the offset the way the more
general "any EE" macro would, and get rid of the unneeded macros.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>