firmware: arm_ffa: Align RxTx buffer size before mapping

firmware: arm_ffa: Align RxTx buffer size before mapping

Commit 83210251fd70 ("firmware: arm_ffa: Use the correct buffer size during
RXTX_MAP") advertises PAGE_ALIGN(rxtx_bufsz) to firmware when mapping the
buffers but the driver continues to stores the minimum FF-A buffer size
in drv_info->rxtx_bufsz which is used elsewhere in the driver.

Align the size before storing it so that the allocation, validation and
FFA_RXTX_MAP all use the same buffer size.

Fixes: 83210251fd70 ("firmware: arm_ffa: Use the correct buffer size during RXTX_MAP")
Cc: Sebastian Ene <sebastianene@google.com>
Link: https://sashiko.dev/#/patchset/20260402113939.930221-1-sebastianene@google.com
Reviewed-by: Sebastian Ene <sebastianene@google.com>
Link: https://patch.msgid.link/20260428-ffa_fixes-v2-9-8595ae450034@kernel.org
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>