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.