linux-postmarketos-allwinner: upgrade to 5.13.1 and optimize kernel config

I'm running on kernel 5.13.1 with optims on my DD pinephone fine since it was released

I've been running all optims since kernel 5.12.11 fine

Optimizations shrunk the uImage from 19.13 MiB to 17.45 MiB

I've run the following benchmark using two PinePhones:

Octane benchmark on Firefox
Devices: Pinephone Beta Edition CE 3GB @528MHz

Kernel 5.12.12 no optims
	PP#1	PP#2
Batt.	55%	31%
run#1	1333	1349
run#2	1334	1275
run#3	1336	1250

avrg.	1334	1291	1312

Kernel 5.12.12 with all optims (FULL PREEMPT)
	PP#1	PP#2
Batt.	53%	51%
run#1	1280	1340
run#2	1284	1286
run#3	1275	1334

avrg.	1279	1320	1299	-13

Kernel 5.12.12 with all optims (Voluntary PREEMPT)
	PP#1	PP#2
Batt.	68%	57%
run#1	1257	1271
run#2	1328	1347	
run#3	1314	1294

avrg.	1300	1304	1302	-10

Kernel 5.13.0 with all optims (FULL PREEMPT)
	PP#1	PP#2
Batt.	53%	45%
run#1	1331	1292	
run#2	1263	1341
run#3	1323	1310

avrg.	1305	1314	1309	-3

Benchmark results are a bit inconclusive but with FULL PREEMPT the UI feel more responsive so I think I'll keep it on

One draw back with FULL PREEMPT is a slower USB transfer (down to ~3MiB/s from ~10MiB/s), that will be solved when Megi has time to enable DMA in the driver