brcmfmac: allow credit borrowing for all access categories

Current credit borrowing allows only the access category BE to
borrow the credits. This change is to fix the credit borrowing
logic, to make borrowing available for all access categories
and also to borrow only from the lower categories. This fixes WFA
802.11n certs 5.2.27 failures.

Signed-off-by: Raveendran Somu <raveendran.somu@cypress.com>
Signed-off-by: Jia-Shyr Chuang <joseph.chuang@cypress.com>
Signed-off-by: Chung-Hsien Hsu <stanley.hsu@cypress.com>
Signed-off-by: Chi-hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200610152106.175257-2-chi-hsien.lin@cypress.com