net: ipa: relax pool entry size requirement

I no longer know why a validation check ensured the size of an entry
passed to gsi_trans_pool_init() was restricted to be a multiple of 8.
For 32-bit builds, this condition doesn't always hold, and for DMA
pools, the size is rounded up to a power of 2 anyway.

Remove this restriction.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>