[arch][arm] Round up to align end of initial mapping to a section.
[arch][arm] Round up to align end of initial mapping to a section.

Allows booting with less than 1MB ram.

Change-Id: I334d2cf14f12194115d64695928333b69632f0fd

nvll/lk,littlekernel/lk,skabet/lk,nvll/lk,ErikCorryGoogle/lk,GCrean/lk,minglun-tsai/lk,sndnvaps/lk,hollanderic/lkstuff,littlekernel/lk,minglun-tsai/lk,nvll/lk,srodrig1/lk,travisg/lk,hollanderic/lkstuff,travisg/lk,GCrean/lk,skabet/lk,skabet/lk,sndnvaps/lk,srodrig1/lk,ErikCorryGoogle/lk,skabet/lk,srodrig1/lk,sndnvaps/lk,srodrig1/lk,nvll/lk,srodrig1/lk,travisg/lk,ErikCorryGoogle/lk,minglun-tsai/lk,nvll/lk,hollanderic/lkstuff,hollanderic/lkstuff,minglun-tsai/lk,GCrean/lk,littlekernel/lk,GCrean/lk,skabet/lk,littlekernel/lk,travisg/lk,sndnvaps/lk,ErikCorryGoogle/lk,sndnvaps/lk,GCrean/lk